System for producing a fully impregnated thermoplastic prepreg

ABSTRACT

A thermoplastic prepreg includes a mat, web, or fabric of fibers and hollow glass microspheres that are positioned atop the mat, web, or fabric of fibers or dispersed therein. The thermoplastic prepreg also includes a thermoplastic polymer that is fully impregnated through the mat, web, or fabric of fibers and the hollow glass microspheres so that the thermoplastic prepreg has a void content of less than 3% by volume of the thermoplastic prepreg. The thermoplastic material is polymerized monomers and oligomers in which greater than 90% by weight of the monomers or oligomers react to form the thermoplastic material.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. patent application Ser. No.16/843,312 filed Apr. 8, 2020, which is a division of U.S. patentapplication Ser. No. 16/172,153 filed Oct. 26, 2018, now U.S. Pat. No.10,717,245, issued Jul. 21, 2020, which is a continuation-in-part ofU.S. patent application Ser. No. 15/944,249 filed Apr. 3, 2018, entitled“SYSTEM FOR PRODUCING A FULLY IMPREGNATED THERMOPLASTIC PREPREG,” nowU.S. Pat. No. 11,198,259, issued Dec. 14, 2021, the entire disclosuresof which are hereby incorporated by reference, for all purposes, as iffully set forth herein. This application is also related to U.S. patentapplication Ser. No. 14/088,034 filed Nov. 22, 2013, titled“FIBER-CONTAINING PREPREGS AND METHODS AND SYSTEMS OF MAKING,” theentire disclosure of which is hereby incorporated by reference, for allpurposes, as if fully set forth herein.

BACKGROUND

The use of fiber-reinforced composites is growing in popularity withapplications in transportation, consumer goods, wind energy, andinfrastructure. Some of the many reasons for choosing composites overtraditional materials such as metals, wood, or non-reinforced plasticsinclude reduced weight, corrosion resistance, and improved mechanicalstrength. Within the field of fiber-reinforced polymeric composites,thermoplastics are increasingly being used in place of thermosets as thematrix resin due to better durability, recyclability, thermoformability,improved throughput, lower material cost, and lower manufacturing cost.

Many continuous fiber reinforced thermoplastic composites are producedfrom impregnated tapes. These impregnated tapes may be unidirectionalfiber tapes that are impregnated with a thermoplastic resin. These canbe layered and thermoformed to produce a wide variety of composites ofthe desired shape and strength. There are significant challengesassociated with producing impregnated tapes at low cost and highquality. Traditionally thermoplastic resins are melted and applied tofibers, but molten thermoplastic resins have very high viscosity and,when combined with the high fiber content that is desired, results inincomplete resin impregnation and/or low throughput. What is desired isa continuous manufacturing process with high throughput that producesfully impregnated thermoplastic prepregs without defects and goodcoupling between the fibers and the matrix resin. For the conventionalpartially impregnated thermoplastic prepregs, high pressure is needed inthe consolidation step to promote additional impregnation, whichintroduces excessive flow of the resin matrix and causes detrimentalchanges in fiber orientation in the finished parts. The fullyimpregnated thermoplastic prepregs of the instant invention areadvantageous in achieving the desired properties in final compositeparts, as no additional impregnation is needed in the consolidationstep.

BRIEF SUMMARY

The embodiments described herein provide fully impregnated thermoplasticprepreg products, and specifically systems and methods for making thesame. According to one aspect, a system for manufacturing athermoplastic prepreg includes a double belt mechanism that includes anupper belt and a lower belt. The upper belt is positioned atop the lowerbelt to compress a fiber mat, web, or fabric and a lightweight fillermaterial that is passed through the double belt mechanism and the lowerbelt has a longitudinal length that is substantially longer than theupper belt. Examples of the lightweight filler material include hollowglass microspheres. The system also includes a drying mechanism that isconfigured to remove residual moisture from the fiber mat, web, orfabric and the lightweight filler material as the fiber mat, web, orfabric and the lightweight filler material are moved past the dryingmechanism. The system further includes an application mechanism that ispositioned atop the lower belt and that is configured to apply the lightweight filler material to the fiber mat, web, or fabric as the fibermat, web, or fabric is moved past the application mechanism. The systemadditionally includes a resin application die that is positioned atopthe lower belt and that is configured to apply monomers or oligomers tothe fiber mat, web, or fabric as the fiber mat, web, or fabric is movedpast the resin application die. The monomers or oligomers arepolymerizable to form a thermoplastic polymer. The system additionallyincludes a curing oven that is configured to effect polymerization ofthe monomers or oligomers and thereby form the thermoplastic polymer asthe fiber mat, web, or fabric and lightweight filler material are movedthrough the curing oven. The double belt mechanism compresses the fibermat, web, or fabric, the lightweight filler material, and the appliedmonomers or oligomers as these materials are passed through the curingoven such that the monomers or oligomers fully saturate the fiber mat,web, or fabric and the lightweight filler material. A full impregnationof the fiber mat, web, or fabric and the lightweight filler materialwith the thermoplastic polymer is thereby achieved upon polymerizationof the monomers or oligomers.

As described herein, full impregnation of the fiber mat, web, or fabricand the lightweight filler material with the thermoplastic polymer meansthat the fiber mat, web, or fabric and the lightweight filler materialare saturated with the thermoplastic polymer so that the fullyimpregnated thermoplastic prepreg has a void content of less than 3% involume based on the total volume of the thermoplastic prepreg. Asdescribed herein, the lightweight filler material may be hollow glassmicrospheres. In such instances, “hollow” interior volume of the hollowglass microspheres is not included in the void content describedabove—i.e., void content of less than 3%. In addition, the hollowinterior of the hollow glass microspheres is not “filled” with thethermoplastic polymer as a person of skill would readily understand.

According to another aspect, a method of forming a thermoplastic prepregincludes moving a fiber mat, web, or fabric atop a lower belt of adouble belt press mechanism and drying the fiber mat, web, or fabric viaa drying mechanism to remove residual moisture from the fiber mat, web,or fabric. The method also includes applying a lightweight fillermaterial to the fiber mat, web, or fabric via an application mechanismthat is positioned atop the lower belt as the fiber mat, web, or fabricis moved past the application mechanism and applying monomers oroligomers to the fiber mat, web, or fabric via a resin application diethat is positioned atop the lower belt. The method further includespassing the fiber mat, web, or fabric, the lightweight filler material,and the applied monomers or oligomers between the lower belt and anupper belt of the double belt press mechanism to press the monomers oroligomers through the fiber mat, web, or fabric and the lightweightfiller material and thereby fully saturate the fiber mat, web, or fabricand lightweight filler material with the monomers or oligomers. Themethod additionally includes passing the fully saturated fiber mat, web,or fabric and lightweight filler material through a curing oven topolymerize the monomers or oligomers and thereby form a thermoplasticpolymer as the fiber mat, web, or fabric and lightweight filler materialare moved through the curing oven. Upon polymerization of the monomersor oligomers, the fiber mat, web, or fabric and lightweight fillermaterial are fully impregnated with the thermoplastic polymer.

According to another aspect, a thermoplastic prepreg includes a mat orweb of fibers and hollow glass microspheres that are positioned atop themat or web of fibers or dispersed therein. The thermoplastic prepregalso includes a thermoplastic polymer that is fully impregnated throughthe mat or web of fibers and the hollow glass microspheres so that thethermoplastic prepreg is substantially free of gaps or voids, whichmeans that the fully impregnated thermoplastic prepreg has a gap or voidcontent of less than 3% in volume based on the total volume of thethermoplastic prepreg. The thermoplastic material is polymerizedmonomers and oligomers in which greater than 90% by weight of themonomers or oligomers react to form the thermoplastic material.

BRIEF DESCRIPTION OF THE DRAWINGS

The present technology is described in conjunction with the appendedfigures:

FIGS. 1A and 1B illustrate systems that may be used to produce prepregsthat are fully impregnated with a thermoplastic polymer.

FIG. 2 illustrates a method of forming a fully impregnated thermoplasticprepreg product.

FIG. 3 illustrates another method of forming a fully impregnatedthermoplastic prepreg product.

FIG. 4 illustrates a SEM micrograph of a cross-section of a fullyimpregnated polyamide-6 prepreg.

FIGS. 5-8 illustrate systems that may be used to produce prepregs thatare fully impregnated with a thermoplastic polymer.

FIG. 8A illustrates a system in which a fiber chopper is replaced with afiber scattering unit.

FIG. 8B illustrates a system that includes a winding mechanism thatwinds a fully cured chopped fiber thermoplastic prepreg into a rollproduct.

FIGS. 9-11 illustrate systems that may be used to produce lighter weightprepregs that are fully impregnated with a thermoplastic polymer.

FIGS. 12-19 illustrate exemplary prepregs that are fully impregnatedwith a thermoplastic polymer.

FIG. 20 illustrates another method of forming a fully impregnatedthermoplastic prepreg product.

FIG. 21 illustrates a method of forming a lighter weight fullyimpregnated thermoplastic prepreg.

FIG. 22 illustrates a graph of a density reduction in a thermoplasticprepreg due to the addition of a lightweight filler material to thethermoplastic prepreg.

In the appended figures, similar components and/or features may have thesame numerical reference label. Further, various components of the sametype may be distinguished by following the reference label by a letterthat distinguishes among the similar components and/or features. If onlythe first numerical reference label is used in the specification, thedescription is applicable to any one of the similar components and/orfeatures having the same first numerical reference label irrespective ofthe letter suffix.

DETAILED DESCRIPTION

Thermoplastic Prepregs

The embodiments described herein relate to fully impregnatedthermoplastic prepreg products, and specifically systems and methods formaking the same. The prepreg products are fully impregnated withthermoplastic materials that allow the prepreg products to be reheatedand molded into a given shape. The prepreg products are made usingreactive resin materials, specifically monomers and oligomers. Forexample, in an exemplary embodiment the resin material is caprolactam,which is extremely sensitive to moisture, wherein even a small amount ofmoisture can affect the anionic polymerization of the caprolactam.Because of the high moisture sensitivity of these materials, achieving ahigh conversion rate of the reactive resin materials to polymers is verydifficult.

In order to achieve a commercially viable prepreg product using monomeror oligomer materials (hereinafter resins, reactive resins, or resinmaterials), the conversion of the reactive resin to a polymer needs tobe greater than 90% by weight and more commonly greater than 95% byweight. A person of skill in the art would recognize, the conversion ofthe reactive resin to a polymer may be readily determined. For example,a residual monomer or oligomer content in the prepreg can be measuredvia a solvent extraction method, which is described herein below.Specifically, when caprolactam is used as the reactive resin, the amountof residual caprolactam in a polyamide-6 (PA-6) prepreg can be measuredvia the extraction of caprolactam from a powder of grounded prepregusing hot water. The conversion of the reactive resin can be deducedbased on the residual monomer or oligomer content. High molecularweights of the thermoplastic polymers are also typically desired. Inpreferred embodiments the resin material comprises caprolactam. Thereactive resin material comprising caprolactam is extremely sensitive tomoisture. The presence of moisture can stop or interfere with theanionic polymerization of caprolactam into a polyamide-6 polymer. Forexample, a moisture content of greater than 200 ppm in the resin cansignificantly interfere with the polymerization process and lower theconversion of the caprolactam material to below 90% by weight. The term“substantially moisture-free” or “substantially zero” in references tohumidity recognizes that some level or amount of humidity may be presentin the air. However, as used herein the term implies that any humiditypresent in the air is negligible, minor, insignificant, or otherwiseinconsequential. For example, a “substantially moisture-free”environment may be created by employing a moisture purge mechanism thatis operable to maintain the relatively humidity in the environment to bebelow 1% at under the temperature range of 5-35° C.

The systems and methods described herein are useful for manufacturingprepreg products using reactive resin materials. The resin conversionrate that is achieved via the systems and methods described herein isgreater than 90% by weight and more commonly greater than 95% by weight.In most embodiments, the conversion rate of the resins is greater than98% by weight or even greater than 99% by weight. As described herein,thermoplastic polymers in the prepreg products are formed via in-situpolymerization, which is not a common technique in manufacturingthermoplastic prepreg products. In addition, the systems and methodsdescribed herein are able to achieve this high conversion rate utilizinga continuous process, wherein a fiber mat, web, or fabric material(woven or nonwoven) is essentially moved constantly or continuallythroughout the manufacturing process. The continuous process greatlyincreases the efficiency of the manufacturing process, which decreasesthe overall cost of the final prepreg product. For example, themanufacturing time between coating of the reactive resin (e.g.,caprolactam) to the formation of a fully impregnated thermoplasticprepreg may be less than 20 minutes and commonly less than 10 minutes.In many embodiments, this processing time may be less than 5 minutes.

The systems and methods described herein are also able to achieve fulland complete impregnation of the prepreg with the thermoplastic polymer.It should be realized that the term “reactive resin” may be used inplace of the term monomers and/or monomers or oligomers within thedescription and/or claims as desired. The viscosity of the reactiveresin at the time when it is applied to a fiber mat, web, or fabric islower than 500 mPa-s, typically lower than 100 mPa-s and more commonlylower than 10 mPa-s. The low viscosity of the reactive resin materialallows that the resin to easily penetrate within and saturate the fibermat, web, or fabric. The low viscosity of the reactive resin allows theresin to flow within and fully saturate either a single layer of thefiber mat, web, or fabric, or multiple layers of these materials.Accordingly, the systems and methods described herein are capable ofproducing prepregs that include multiple layers of materials with eachlayer being fully saturated or impregnated with the thermoplasticpolymer materials. The final prepreg product can be made flexible withhigh content of reinforcing fibers. Because the prepreg products areflexible, the prepregs may be rolled into a rolled product.

The embodiments described herein provide a process and apparatus thatutilizes mixing of reactive resin components, followed by application ofthe reactive resin components to a fiber mat, web, or fabric which maybe formed from the various fiber materials described herein. Thereactive resin components are then cured in an oven to form a fullyimpregnated prepreg having a thermoplastic polymer matrix. In a specificembodiment, caprolactam is polymerized to form polyamide-6 in thefinished prepreg. The system is designed to isolate the reactive resincomponents from atmospheric moisture in order to achieve high conversionfrom monomer to polymer. Specifically, the system is designed to ensurea substantially moisture-free environment in the vicinity of thereactive resin coated fiber mat, web, or fabric. The systems and methodsdescribed herein are designed to isolate the reactive components fromatmospheric moisture in order to achieve high conversion from monomer topolymer. This is achieved, in part, by controlling the environment inthe vicinity of the production process and/or by removing residualmoisture from the fiber mat, web, or fabric and/or any of the processingsystems.

As used herein, the reactive resin means the resin materials thatcomprise monomers or oligomers capable of polymerizing to formthermoplastic polymers. The reactive resins may include lactams such ascaprolactam and laurolactam and lactones. In an exemplary embodiment,the reactive resin comprises caprolactam. In some embodiments, mixturesof monomers and/or oligomers may be used. For example, mixture ofcaprolactam and laurolactam may be used, which will copolymerize in thecuring oven to form copolymers with tailored properties. As used herein,the activator may be any material that activates and accelerates thepolymerization of monomers or oligomers. Exemplary activators for theanionic polymerization of caprolactam include blocked isocyanates andN-acylcaprolactams. As used herein, the catalyst may be any materialthat catalyzes the polymerization of monomers or oligomers. Exemplarycatalysts for the anionic polymerization of caprolactam include alkalinesalt of caprolactam such as sodium caprolactamate.

Various terms are used herein to describe fiber-based products. Forexample, the term “fabric” is used in the application to describefiber-based woven products. The application includes the following termsto describe fiber-based nonwoven products: mat, web, mesh, and the like.It should be understood that these terms may be used interchangeably inthe embodiments. Unless specifically claimed, the disclosure is notlimited to any one particular fiber-based product. Accordingly, it iscontemplated that the terms may be replaced or changed in any of theembodiments described without departing from the intended scope ofdescription. Furthermore, the term “fiber mat, web, or fabric” or“fiber-based product” may be substituted in the description or claimsand is intended to cover any and all fiber-based products or componentsthat are described or contemplated herein.

A common type of fiber that is used in the fiber mat, web, or fabric isglass fibers, although various other fibers could be used such as carbonfibers, basalt fibers, metal fibers, ceramic fiber, natural fibers,synthetic organic fibers such as aramid fibers, and other inorganicfibers. The term fabric as used herein refers to woven materials. Thewoven materials are materials that are produced by weaving multipleroving strands together. The term roving as used herein refers to abundle of fibers that are positioned adjacent one another to form arope, thread, or cord like component. The roving strands are commonlywoven so that a first plurality of strands extend in a first direction(e.g., weft direction) and a second plurality of strands extend in asecond direction that is typically orthogonal to the first direction(e.g., warp direction). The first plurality of strands are roughlyparallel with one another as are the second plurality of strands. Thewoven fabrics or cloths may be unidirectional, where all or most of theroving strands run or extend in the same direction, or may bebidirectional, wherein the roving strands run in two, typicallyorthogonal, directions. Various weaves may be used to form the fabricsdescribed herein, including: plain weaves, twill weaves, satin weaves,multiaxial weaves, or stitching. The woven cloths or fabrics that areemployed may contain any kind of woven fabric or multi-axial fibermaterial. The fabrics or mats may also contain chopped fibers inaddition to or alternatively from the continuous fibers. The fabrics maybe a hybrid from different type of fibers. For ease in describing theembodiments herein, the embodiments will generally refer to the use ofglass fibers, although it should be realized that various other fibertypes may be used.

The term mat as used herein refers to nonwoven materials. As brieflydescribed above, nonwoven fiber mats are used in addition to or in placeof the woven reinforcement fabrics. The nonwoven fiber mats are commonlyformed of fibers that are mechanically entangled, meshed together, orchemically bonded, rather than being woven in a uniform direction. Thenonwoven fiber mats exhibit more uniform strength characteristics incomparison to the woven reinforcement fabrics. Stated differently, thestrength of the nonwoven fiber mats is typically less directionallydependent. In comparison, the strength of the woven reinforcementfabrics is directionally dependent whereby the fabrics or cloths exhibitsubstantially more strength in a direction aligned with the fibers andless strength in a direction misaligned from the fibers. Thereinforcement fabrics or cloths are substantially stronger than thenonwoven mats when the tension is aligned with the fibers. For ease indescribing the embodiments herein, the embodiments will generally referto fabrics or mats, which is intended to apply to both woven fabrics orcloths and nonwoven fiber mats.

The fibers used in the fabrics or mats may be treated with a sizingcomposition including coupling agent(s) that promote bonding betweenreinforcing fibers and polymer resin. For example, the fibers may besized with one or more coupling agents that covalently bond thethermoplastic resin to the fibers. Exemplary coupling agents may includecoupling-activator compounds having a silicon-containing moiety and anactivator moiety. Specific examples of coupling-activator compoundsinclude 2-oxo-N-(3-(triethoxysilyl)propyl)azepane-1-carboxamide.Exemplary coupling agents may also include blocked isocyanate couplingcompounds having a silicon-containing moiety and a blocked isocyanatemoiety. Exemplary coupling agents may also include coupling compoundshaving a functional group that may react with the reactive resin to formcovalent bond. Specific example of the coupling compounds having afunctional group include silane coupling agent having amino, epoxy, orureido functional groups.

The term thermoplastic polymer or material refers to polymers that arecapable of being melted and molded or formed into various shapesmultiple times. As such, the fully impregnated thermoplastic prepregsmay be positioned in a mold and reformed or remolded into variousdesired shapes. Examples of polymer materials or resins that may be usedwith the embodiments herein include polyamides, specifically includingpolyamide-6.

The description and/or claims herein may use relative terms indescribing features or aspects of the embodiments. For example, thedescription and/or claims may use terms such as relatively, about,substantially, between, approximately, and the like. These relativeterms are meant to account for deviations that may result in practicingand/or producing the embodiments described herein. For example, thedescription describes mixtures from two holding tanks as being mixedinto a “substantially homogenous mixture”. The disclosure also describespurging a fiber mat, web, or fabric with “a substantially moisture-freegas” and that the fiber mat, web, or fabric is in “substantiallyconstant movement” between a starting point and ending point. The term“substantially” is used in these descriptions to account for smalldeviations or differences from a complete homogenous mixture, or acompletely moisture-free gas, or an entirely constant movement. Forexample, a skilled artisan would recognize that the moisture-free gasmay include some negligible amount of moisture and that some negligibleamount of non-homogeneity may be present within the homogenous mixture.The skilled artisan would also recognize that some negligible stoppageor non-movement of the fiber mat, web, or fabric may occur withoutdeparting from the spirit of the disclosure herein. These deviations ofdifferences may be up to about 10%, but are typically less than 5%, oreven 1%. A similar rationale applies to any of the other relative termsused herein.

In producing conventional thermoplastic prepregs, the process of fullyimpregnating or saturating the fiber mat, web, or fabric is ratherexpensive and/or difficult due to the high melt viscosity of thethermoplastic resin. In some instances, a solvent is added to thepolymer resin/thermoplastic material to reduce the viscosity of thematerial. While the reduced viscosity may add in fully impregnating thereinforcement fabric, the solvent needs to be subsequently removed fromthe fabric after the polymer resin/thermoplastic material is impregnatedwithin the fabric. Removal of the solvent commonly involves heating thefabric to evaporate the solvent, adding cost and environmental concerns.In contrast to these systems, no solvent is used in the reactive resinmixture described herein.

Other conventional technologies use pre-impregnated thermoplastic tapesof polymer resin and reinforcing fibers. These tapes are typicallymanufactured as a single layer by applying a molten polymer resin atopflattened rovings. For example, glass rovings may be passed over rollersto flatten and spread fibers that are then coated with a molten polymerresin. The tapes are then cooled with the glass fibers encased withinthe hardened polymer resin material. The tapes may then be used inproducing other products, typically by stacking and welding severallayers of tape together. The process of spreading fibers for resinimpregnation typically limits to rovings; since spreading fibers infabrics or mats is nearly impossible. In addition, the stacked tape isoften rigid, which makes it difficult to mold intricate shapes.

In contrast to conventional prepregs, the production of thethermoplastic prepregs described herein is fast and simple. For example,fully saturating the fiber mat, web, or fabric is relatively easy sincethe reactive resin materials (e.g., caprolactam) have a low viscositythat is comparable to water. This low viscosity allows the resinmaterials to easily flow within and fully saturate a single or multiplelayers of the fiber mat, web, or fabric. The capillary force of therovings or fibers further aids in saturating the fiber mat, web, orfabric. The low viscosity of these materials also allows the materialsto be applied to a constantly or continually moving sheet of material.The resins may then be converted into a thermoplastic polymer materialso that the fiber mat, web, or fabric is fully impregnated with thethermoplastic material.

While the embodiment herein generally refers to the manufacture ofpolyamide-6 prepregs, other reactive resin systems can be easily adaptedto work with the same or similar apparatus to form thermoplasticprepregs including other types of polyamides and blends of thermoplasticpolymers such as the blends of polyamides and polyesters.

Having described several aspects of the embodiments generally,additional aspects will be evident with reference to the description ofthe several drawings provided below.

Thermoplastic Prepreg Systems

Referring now to FIGS. 1A and 1B, illustrated is a system that may beused to produce prepregs that are fully impregnated with a thermoplasticpolymer. The systems of FIGS. 1A and 1B are capable of producing thefully impregnated thermoplastic prepregs in a continuous process,wherein a fabric or mat 4 is continually or constantly in movementthrough the system. Stated differently, the term continuous processmeans that the process is not interrupted or paused in performing anyone process step. Rather, each step in the process is continually orconstantly being performed. For example, the fabric or mat iscontinually moved from a rolled good, coated with the resin material,cured in the oven, and rolled into a final product. In contrast,conventional systems typically are halted or interrupted during theperformance of one or more steps, such as the impregnation of fibroussubstrates with high melt viscosity thermoplastic polymer resin.

In some embodiments, the system includes two vessels or holding tanks(i.e., 1 and 2 2). The holding tanks, 1 and 2, may be heated and purgedwith nitrogen to ensure the removal of any moisture, which couldotherwise reduce the reactivity of the raw materials and consequentlyreduce the conversion of the resins to a polymer. One of the holdingtanks (e.g., holding tank 1) may contain a mixture of a resin and acatalyst. In a specific embodiment, the holding tank (e.g., tank 1)includes caprolactam and a catalyst, such as sodium caprolactamate orany other catalyst. The other holding tank (e.g., tank 2) may contain amixture of the resin and an activator. In a specific embodiment, theother holding tank (e.g., tank 2) includes caprolactam and an activator,such as N,N′-hexane-1,6-diylbis(hexahydro-2-oxo-1H-azepine-1-carboxamide) or anyother activator. The holding tanks, 1 and 2, are heated to a temperaturethat allows the reactants to melt. In some embodiments, the temperaturemay be between about 70 and 120° C. The molten reactants (e.g., theresin and activator or catalyst) have a very low viscosity, for example,lower than 10 mPa-s.

The reactants from the two holding tanks, 1 and 2, are metered into astatic mixer or mixing head 3 that ensures the correct ratio of theresin, activator, and catalyst. In one embodiment, the mixtures from thetwo holding tanks, 1 and 2, may be provided to the static mixer in a 1/1ratio. The mixtures from the two holding tanks, 1 and 2, are thoroughlymixed in the static mixer 3 into a substantially homogenous mixture.

In some other embodiments, the system includes single or multiplevessels or holding tanks. Each of the vessels or holding tanks maycontain individual components or mixtures of the reactive resinmaterials. Each of the vessels or holding tanks are heated to atemperature that allows the reactants to melt.

A fabric or mat 4 is unwound or otherwise provided to the system. Thesystem may include a mechanism that unwinds the fabric or mat and movesthe fabric or mat through the system and along or about the variousprocesses. In some embodiments, the mechanism may include poweredrollers or calendars and/or a conveyor system, that move the fabric ormat through the system.

In some embodiments, the activator is included on the surface of thefibers. The fabric or mat may consist of glass fibers that have beenpre-treated with a sizing composition. For example, the sizingcomposition may include a coupling activator that covalently bonds thepolymerization activator moiety to the glass fiber. In such instances,the bonding between the thermoplastic polymer and the fibers may besignificantly strengthened or enhanced. When the fabric or mat includesthe activator, only a single holding tank (e.g., tank 1) containing theresin and catalyst may be used, or a reduce amount of the activator maybe mixed with the resin in the second holding tank (e.g., tank 2). Insome embodiments, two holding tanks, 1 and 2, may be used and eachholding tank may include a different resin material. For example, afirst holding tank 1 may include caprolactam while the second holdingtank 2 includes laurolactam. In such instances, a combination of two ormore types of reactive monomers and/or oligomers may be applied to thefabric or mat.

In a specific embodiment, the fiber sizing contains a mixture of silanecoupling agents, polymeric film formers, and other additives that aredesigned to enhance the interfacial bonding between the glass fiber andpolyamide-6 matrix. Specifically, a reactive silane is used that allowssome of the polymerization to be initiated directly from the glasssurface, thus improving the coupling between the reinforcing fibers andthe resin matrix to improve composite properties.

After the fabric or mat 4 is unwound, or during the unrolling of thefabric or mat, the fabric or mat may be subjected to a drying mechanismthat removes residual moisture from one or more surfaces of the fabricor mat. For example, an infrared heater 5 may be used to raise thetemperature of the fiber mat, web, or fabric and thereby remove anyresidual moisture. In a specific embodiment, the infrared heater 5 maybe positioned atop or over the fabric or mat 4 to remove residualmoisture. In some embodiments, a second heater can be positioned on anopposite side (e.g., bottom side) of the fabric or mat 4 to further aidin removal of residual moisture. In other embodiments, a pre-drying ovenmay be used in place of or in addition to the infrared heater 5. Thepreheating of the fabric or mat 4, and/or the preheating of the resin,may be employed to prevent the monomer/oligomer from solidifying uponcontact with the fibers of the fabric or mat, which may ensure a goodwet out of the resin at higher line speeds.

The resin mixture is then applied to the fabric or mat 4 using a resinapplication die 6 or other resin application mechanism. The resinapplication die 6 may be a slot die. The slot die 6 may be positionedatop or adjacent one or more surfaces of the fabric or mat 4. The resinmixture is typically applied as close as possible to an inlet of thecuring oven 8 in order to minimize exposure of the resin material to thesurrounding air. To minimize exposure to the surrounding air, the slotdie 6 may be positioned directly adjacent to the inlet of the curingoven 8. In some embodiments, the slot of the slot die 6 may have anopening of about 1.0 mm or less that enables the use of a very thin die.The thin die allows the distal end of the die to be positionedsubstantially close to the curing oven 8 to minimize the exposure of theresin mixture to the surrounding environment. In some embodiment, thedistal end of the slot die 6 may be positioned within 1.0 inches of thecuring oven's inlet, and preferably within 0.5 inches of the inlet. Theslot die 6 may be temperature controlled within a temperature rangeabove the melting point of the reactive resin. For the reactive resincomprising caprolactam, the temperature range may be between 70° C. and120° C. The slot die 6 may include a thermocouple and heating cartridgeor other heating component to ensure that the slot die 6 remains withinthe desired temperature range.

While the embodiment herein utilizes a slot die 6 for application of theresin mixture to the fabric or mat 4, the low viscosity of such systemsallows a wide range of application technologies including, but notlimited to, spray application, curtain coating, dip and squeeze coating,kiss roll application, doctor blade application, or even powder coatingof pre-ground solid resins where the curing oven can also be utilized tomelt the reactive components.

The liquid handling lines between the two holding tanks, 1 and 2, andthe static mixer 3 and/or between the mixer 3 and the slot die 6 aretypically insulated to minimize heat loss as the resin mixtures flowthrough the handling lines. In some embodiments, the liquid handlinglines are heated in addition to being insulated to ensure that theliquid materials (e.g., resins, catalyst, and activator) are maintainedwithin a constant temperature range. Specifically, the liquid transportlines between the holding tanks, 1 and 2, (or solitary holding tank) andthe mixer 3 and/or between the mixer 3 and the slot die 6 are insulatedand heated to maintain the liquid materials within a temperature rangeabove the melting point of the reactive resin. Controlling thetemperature of the liquid materials ensures that the resin does notsolidify and/or prematurely react within the handling lines.

In the above process, the temperature of the resin is typicallymaintained within a temperature range above the melting point of thereactive resin in order to maintain the resin in a liquid or moltenstate while preventing premature polymerization of the resin prior tothe curing of the material in the oven. The resin components may need tobe recirculated, such as between one or more holding tanks, 1 and 2, andthe mixer 3. Ensuring that the resin is maintained with a desiredtemperature range is important to minimizing or eliminating prematureresin polymerization and/or material build up in the system and/orliquid handling lines.

Of equal importance is the controlling the surrounding environment inthe vicinity of the coated fabric or mat 4 to ensure that the resinmixture is not exposed to ambient moisture. Exposure of the resinmixture to ambient moisture may reduce the conversion of the resin,which may result in a resin to polymer conversion rate of less than 90%.The systems of FIGS. 1A and 1B are designed to isolate the resin mixture(i.e., reactive components) from atmospheric moisture in order toachieve high conversion from monomer/oligomer to polymer. In someembodiments, the entire system may be housed or enclosed in a room orarea in which the environment is controlled to maintain a substantiallymoisture-free environment. Various dehumidification techniques can beused to remove moisture from the ambient air in the room or area.Exemplary dehumidification techniques include desiccantdehumidification, refrigerant dehumidification, and electrostaticdehumidification. In other embodiments, the system may employ a moisturepurge mechanism that is operable to ensure that the humidity in the airsurrounding the coated fabric or mat is substantially zero. In suchembodiments, the moisture purge mechanism need be employed only in thevicinity of the slot die 6 since the fabric or mat 4 is free of theresin material prior to this point. The moisture purge mechanism may bepositioned proximally of the slot die 6 or distally of the slot die 6 asdesired. In either instance, however, the moisture purge mechanismshould be positioned relatively close to the slot die 6 to minimizeexposure of the resin mixture to the surrounding air. For example, thesystem may be enclosed in an area that is purged with a substantiallymoisture-free gas.

In a specific embodiment, the moisture purge mechanism includes anair/gas plenum or tube 7 of FIG. 1A that blows a moisture-free gas ontoone or more surfaces of the coated fabric or mat 4. The air/gas plenumor tube 7 may be positioned atop the fabric or mat 4, or may bepositioned on opposite sides of the fabric or mat as desired. In aspecific embodiment, the air/gas plenum or tube 7 blows dry nitrogenatop or across either or both the top surface or the bottom surface ofthe fabric or mat 4. The air/gas plenum or tube 7 ensure that the areaor vicinity around or adjacent the coated fabric or mat 4 and/or in thevicinity of the curing oven's inlet is kept substantially free ofmoisture. Minimizing the exposure of the resin material to moisture iscritical to ensuring a high conversion rate of the resin material.Accordingly, the use of the drying mechanism (e.g., infrared heater 5)and/or moisture purge mechanism (e.g., air/gas plenum) is important toensuring proper manufacturing of the prepreg. In another specificembodiment, the resin application mechanism as well as the coated fabricor mat may be enclosed in a box 7, as shown in FIG. 1B, that is purgedwith a substantially moisture-free gas.

After the fabric or mat 4 is coated and/or saturated with the resinand/or purge gas is applied to one or more surfaces of the coated fabricor mat 4, the resin impregnated fabric or mat 4 is then passed through acuring oven 8. The temperature of the curing oven 8 is maintained toensure the completion of the polymerization of the resin to athermoplastic polymer. Stated differently, the curing oven 8 ismaintained at a polymerization temperature at which the monomers and/oroligomers start to polymerize. For a reactive resin composition thatincludes caprolactam, the polymerization temperature may be about 120°C. or more (e.g., about 120° C. to about 220°). For prepregmanufacturing processes where the polymerized resin matrix is notmelted, an upper limit on the polymerization temperature for themonomers and/or oligomers may be the melting temperature of the polymer.For example, a reactive resin composition that includes caprolactam mayhave a upper limit of a polymerization temperature that is the meltingtemperature of the PA-6 polymer (i.e., ˜220° C.). The coated fabric ormat 4 may be exposed to the curing oven 8 for a time which is sufficientto ensure complete polymerization of the resin material. For example,for a reactive resin composition that includes caprolactam, theresidence time of the coated fabric or mat in the curing oven may beabout 3 minutes to ensure the complete polymerization of caprolactam.

As noted above, when the reactive resin composition is a combination oftwo or more types of reactive monomers and/or oligomers, the heatingtemperature of the resin-fiber mixture may be chosen to be above athreshold polymerization temperature of one type of monomer/oligomer butbelow a threshold polymerization temperature of the other type ofmonomer/oligomer. For example, a reactive resin composition thatincludes both caprolactam and CBT may be heated to 120-170° C., whichmay polymerize the caprolactam to PA-6 without significantlypolymerizing the CBT to polybutylene terephthalate (PBT). The resultingfiber-resin amalgam will include a polymerized resin matrix of PA-6combined with a polymerizable resin of CBT. The fiber-resin amalgam maybe processed into a reactive prepreg that includes a polymerized resinmatrix of PA-6 and polymerizable CBT. The reactive prepreg may beincorporated into a fiber-reinforced article, where the processingconditions may include polymerizing the CBT into PBT. In otherembodiments, mixtures of monomers and/or oligomers may be used. Forexample, a mixture of caprolactam and laurolactam may be used, whichwill copolymerize in the curing oven to form copolymers with tailoredproperties.

In some embodiments, the coated fabric or mat 4 is subjected to a pressmechanism that facilitates in complete wet-out of the reinforcing fibersby the resin. In one embodiment, the press mechanism may include one ormore calendars that press or squeeze the resin through the fabric or mat4. In another embodiment, the curing oven 8 may be a double beltcompression oven where the pressure on the belts is adjustable tofacilitate complete wet-out of the reinforcing fibers by the resin. Theexposure of the coated fabric or mat to ambient moisture may beminimized by using double belt press that is oil or electrically heated.

Upon exiting the curing oven 8, the fully cured prepreg 9 may becollected. In some embodiments, the system includes a winding mechanismthat is configured to wind the fully cured prepreg 9. In otherembodiments, the fully cured prepreg may be cut into sheets, which maybe stacked atop one another.

The systems of FIGS. 1A and 1B are designed so that the above process isable to be performed in a time of 20 minutes or less, and more commonly10 minutes or less. In some embodiments, the process may be performed in5 minutes or less. Specifically, the time period between when the fabricor mat 4 is initially unwound to when the prepreg exits the curing oven8 may be 20 minutes or less, 10 minutes or less, or in some embodiments5 minutes or less. This speed and impregnation efficiency is notachievable via conventional systems using polymer resin materials.Moreover, the speed and efficiency is not drastically affected whenmultiple stacked layers of the fabric or mat 4 are employed. Rather, thelow viscosity resin mixture is able to easily penetrate through andsaturate the multiple stacked layers of the fabric or mat 4 so that theprocessing time of the stacked layers of the fabric or mat remains low.Full impregnation of the stacked layers of the fabric or mat 4 isachievable due to the low viscosity of the resin materials.

Thermoplastic prepregs, which are sometimes referred to as anorganosheets, offer some superior properties such as impact resistance,thermoformability, and recyclability, as compared to thermoset prepregs.Because of the directionality of fiber orientation in fabrics, however,conventional thermoplastic prepregs have anisotropic mechanicalproperties, which poses significant challenges in designing compositeparts to replace incumbent isotropic materials such as steel andaluminum. In addition, fabric-based thermoplastic prepregs may havelimited conformability, which may increase the difficulty in formingcomposite parts with complex geometry.

Hybrid Thermoplastic Prepregs

As described herein, in some embodiments the thermoplastic prepreg maybe formed of chopped strands or fibers (hereinafter chopped fibers).Specifically, the fiber material in the prepreg may comprise or consistof chopped fibers. The use of chopped fibers in a thermoplastic prepregsmay result in a prepreg with more isotropic mechanical properties andincreased conformability, while maintaining high strength and impactresistance. Such thermoplastic prepregs may be formed in a continuousmanufacturing process that may include: (I) in-line chopping rovingsinto long fibers or strands, which are dispensed uniformly onto a movingbelt to form an un-bonded chopped strand mat; (2) impregnating thechopped fiber or strand mat with a reactive resin such as moltencaprolactam; (3) pressing the coated chopped fiber or strand mat tofully saturate the mat with the reactive resin (e.g., caprolactam); and(4) in-situ polymerizing the reactive resin in an oven to form thechopped fiber or strand thermoplastic prepreg. To ensure the fullpolymerization of the reactive resin, and in particular caprolactam, thefibers or rovings may be in-line dried prior to chopping, and thechopped fiber or strand mat may be further dried prior to theimpregnation with the reactive resin (e.g., caprolactam). The system istypically further configured to maintain a moisture free environment inthe vicinity of the reactive resin coated chopped fiber or strand matprior to subjecting the reactive resin coated chopped fiber or strandmat to the curing oven. Maintaining a moisture free environmentsubstantially prevents exposure of the reactive resin, and in particularcaprolactam, to moisture.

The term chopped fibers relates to fibers that are chopped fromcontinuous rovings or tows. Chopped fibers may have length from 10 mm to100 mm, preferably from 25 mm to 50 mm. The fibers that are employedherein may be selected from, but are not limited to, the following typesof fibers: glass fibers, carbon fibers, basalt fibers, polymer fibersincluding aramid, natural fibers including cellulosic fibers, and otherinorganic fibers. The fibers can be treated with coupling agents, whichmay improve interfacial bonding between fibers and thermoplastic resinmatrix.

The chopped fibers typically form a chopped fiber or strand mat, whichis a fiber mesh or web of unbonded chopped fiber segments. The termun-bonded implies that the mesh or web of chopped fibers is notmechanically or chemically coupled or bonded together, or coupledtogether via some other means. On the other hand, nonwoven matstypically comprise fibers randomly laid atop one another and bonded orcoupled together with an applied binder or adhesive. In otherembodiments, mechanically coupling may be used in place of chemicalcoupling. Mechanically coupling of the fibers may be achieved bymechanical needling in which a needle or rod is inserted into the fiberweb to encourage or effect entanglement of the fibers. In someinstances, nonwoven mats may include both chemical and mechanicalcoupling of the fibers. Woven fabrics or mats are mechanically coupledtogether via the weaving of the fiber rovings or tows together.

In contrast to these conventional nonwoven mats, in the instantapplication the web or mesh of chopped fibers is unbonded so thatindividual chopped fibers are not chemically or mechanicallybonded—i.e., a binder or adhesive is not employed nor are mechanicalbonding techniques, such as mechanical needling. Rather, the choppedfibers are merely laid atop one another with minimal physicalengagement. The result is that, prior to the addition of the reactiveresin, the web or mesh of chopped fibers may be easily separated orpulled apart, such as by the application of a gas over the fiber web ormesh. It should be appreciated that a minimal degree of physicallyentanglement or engagement will likely be encountered due to the randomorientation of the chopped fibers in the web or mesh, but that ingeneral the chopped fibers remain uncoupled or unbonded from one anotherso that the web or mesh has minimal structural integrity prior toapplication of the reactive resin and the subsequent polymerization toform thermoplastic polymer.

Once the reactive resin has been added to the chopped fiber web or mesh,the thermoplastic polymer resulted from in-situ polymerization of thereactive resin may function to bond or adhere the chopped fiberstogether. Thus, the thermoplastic polymer functions as the adhesivematrix that bonds or adheres the chopped fibers together. In someembodiments, the chopped fiber web or mesh may be used with a fabric ornonwoven mat, such as those described herein. In such embodiments, thechopped fiber web or mesh may be positioned on a single side or bothsides of the fabric or nonwoven mat. Because of the very low viscosityof thermoplastic resin that is commonly employed (e.g., caprolactam),complete impregnation of the chopped fiber web or mesh is easilyachieved in a short period of time, which ensures a high-volumemanufacturing process. Thus, the process described herein hassignificant advantages in both production efficiency and compositeproperties, as compared to conventional polymer melt-impregnationprocesses in which highly viscous polymeric resin melts are used toimpregnate reinforcing fibers.

While the description herein generally refers to the use of an un-bondedchopped fiber web or mesh, it should be appreciated that in someinstances it may be desirable to couple the chopped fibers together viachemical means, mechanical means, or some other means. The reactiveresin may then be added to the coupled or adhered chopped fiber web ormesh. To simplify the description of the various embodiments, thechopped fiber web or mesh will be generally referred to as a choppedfiber web or mesh or more simply a fiber web or mesh. This generaldescription of a chopped fiber web or mesh is meant to describe both anun-bonded or non-adhered chopped fiber web or mesh as well as a bondedor adhered chopped fiber web or mesh. The use of the term in the claimsis likewise meant to cover both the un-bonded/non-adhered chopped fiberweb or mesh as well as the bonded or adhered chopped fiber web or meshunless the claims specifically recite one of these fiber webs or meshes.Thus, the generic description of a chopped fiber web or mesh in thedescription and/or claims may be substituted with the more specificdescription of an un-bonded or non-adhered chopped fiber web or mesh ora bonded or adhered chopped fiber web or mesh if desired.

The resulting chopped fiber thermoplastic prepreg comprises randomlyoriented chopped fibers and possess largely isotropic mechanicalproperties. Due to the excellent conformability of the chopped fibers,the chopped fiber thermoplastic prepreg described herein is capable ofbeing formed into complex-shaped composite parts with deep draws andlarge curvatures, via high throughput processes such as compressionmolding. Additional aspects and features of the chopped fiberthermoplastic prepreg will be appreciated in regards to the descriptionof the various embodiments provided below.

Lightweight Prepreg

In some embodiments it may be desirable to decrease the density of thethermoplastic prepreg. Such prepregs may be generally referred to aslightweight prepregs, since they are lighter in density thanconventional prepregs. Lightweight prepregs may be particularly usefulin applications where weight is an issue or concern. The density of thethermoplastic prepreg may be reduced by adding a lightweight fillermaterial to the thermoplastic prepreg. The term “lightweight fillermaterial” means a material that has a density of between 0.1 and 1.0g/cm³. The density of lightweight filler material is determined per ISO12154:2014 test method. In a specific embodiment the lightweight fillermaterial may be hollow glass microspheres, which are also commonlyreferred to as glass bubbles. In other embodiments, the lightweightfiller material may be perlite or other lightweight materials.

The use of the lightweight filler material results in thermoplasticprepregs that have a reduced density in comparison with conventionalthermoplastic prepregs. The lightweight thermoplastic prepregs exhibithigh strength and impact resistance despite the reduced density. Unlikeconventional systems that introduce filler materials with the polymerresin and fibers in an extrusion processes, the systems described hereinare able to introduce the lightweight filler material to the prepregfibers without fiber attrition. The extrusion process employed inconventional systems typically breaks the fibers into much shorterlengths. The thermoplastic prepregs that are formed from the systemsdescribed herein may include fibers that are significantly longer inlength than those of conventional thermoplastic composites produced viaan extrusion process. For example, the thermoplastic prepregs that areformed from the systems described herein may include fibers that are 10mm or longer; while the conventional thermoplastic composites that areformed via an extrusion process may include fibers that are 1 mm orshorter.

The reinforcement components that are used in conventional thermoplasticprepregs, including glass fibers, have higher density than thermoplasticresin. For example, the glass fibers that are employed in thermoplasticprepregs typically have a density of around 2.6 grams per cubiccentimeter (g/cm³). For applications such as automotive, the density andweight of components is critical for fuel efficiency.

In order to reduce the density of the prepregs, a light weight fillermaterial may be added to the thermoplastic prepreg. For example, hollowglass microspheres commonly have densities ranging from 0.10 to 0.60g/cm³ and are therefore, significantly lighter than both the fibers andpolymer materials of conventional thermoplastic prepregs. In somepreferred embodiments, hollow glass microspheres that may be employedhave a density lower than 0.40 g/cm³.

Since the lightweight filler material is significantly lighter in weightthan both the glass fibers and polymeric material, adding an appreciableamount of the lightweight filler material to the thermoplastic prepregsubstantially reduces the overall density of the thermoplastic prepreg.The lightweight filler material reduces the overall density of thethermoplastic prepreg by occupying a volume or space within the prepregthat would otherwise by filled or occupied by the heaver glass fiberand/or polymeric materials. The weight percentage of hollow glassmicrospheres in the thermoplastic prepreg may be between 1% and 30%,preferably between 2% and 20%, and more preferably between 3% and 10%,based on the total weight of the prepreg.

In some embodiments, the lightweight filler material may be added to thereactive resin described herein (e.g., monomers and/or oligomers) sincethe viscosity of the reactive resin in the molten state is very low. Forexample, the viscosity of the reactive resin that includes caprolactamis lower than 10 mPa-s at 80° C. In conventional systems, thelightweight filler material typically cannot be added to thethermoplastic polymer materials because the viscosity of such materialsis substantially greater than the reactive resins described herein(i.e., substantially greater than 10,000 mPa-s). The low viscosity ofthe reactive resin enables the lightweight filler material to be mixedwith the reactive resin and subsequently applied to the fiberreinforcement materials through various methods, such as via a slot die,curtain coater, roller coater, spray nozzle or mechanism, and the like.In other embodiments, the hollow glass microspheres may be combined withthe reinforcing fibers prior to the application of the reactive resin.For example, a microsphere application mechanism may be positioned abovethe fabric, mat, web, or mesh so that the hollow glass microspheres areapplied atop or within the fabric, mat, web, or mesh. The reactive resinmay then be applied to the fiber mat, web, or mesh that incorporates thehollow glass microspheres. The thermoplastic prepreg may be formed viain-situ polymerization of the reactive resin.

In some embodiments, the lightweight filler material may include acoating that facilitates bonding between the filler material and thethermoplastic resin. For example, a silane coating may be added to thesurface of the hollow glass microspheres to increase the interfacialstrength between the microspheres and resin matrix. In addition to beinglightweight, the glass microspheres exhibit excellent strengthproperties and thus, the use of the hollow glass microspheres in thethermoplastic prepreg do not significantly negatively affect thestrength properties of the prepreg. FIG. 22 illustrates a graph showingthe density reduction in comparison with the weight percentage of hollowglass microspheres that are present within the thermoplastic prepreg. Asillustrated, the density of the thermoplastic prepreg (e.g., glass fiberreinforced polyamide-6 prepreg) was reduced by the introduction of thehollow glass microspheres (e.g., Glass Bubbles S38HS sold by 3M™) intoprepreg. In FIG. 22 , the density of the thermoplastic prepreg wasreduced from about 1.90 g/cm³ to about 1.00 g/cm³ as the weightpercentage of the hollow glass microspheres increased from 0.0 percentto about 20 percent. The density of the thermoplastic prepreg containinghollow glass microspheres is typically lower than 1.8 g/cm³, preferablylower than 1.5 g/cm³, and more preferably lower than 1.3 g/cm³. Thereduction in density was very dramatic for the amount of hollow glassmicrospheres that were added to the thermoplastic prepreg. The resincontent of the thermoplastic prepreg of FIG. 22 was roughly 30 percentby weight and the density of the hollow glass microspheres was roughly0.38 g/cm³.

The lightweight filler material may be homogenously dispersed throughoutthe thermoplastic prepreg; may form a layer on top of the fabric, mat,web, or mesh; or may be sandwiched between opposing layers of fabric,mats, webs, or meshes. The penetration of the lightweight fillermaterial into the fabric, mat, web, or mesh may depend on how looselythe fibers are positioned in relation to one another. For example,hollow glass microspheres may be able to easily penetrate into thefabric, mat, web, or mesh when the fibers are relatively loose inrelation to each other. In other embodiments, the lightweight fillermaterial may be combined with chopped fibers in a hopper. The choppedfibers and lightweight filler material may be scattered or dispersed viaa fiber scattering unit. In yet other embodiments, the filler materialapplication mechanism may be positioned immediately adjacent a fiberchopper or fiber scattering mechanism so that the lightweight fillermaterial is added relatively homogenously to the chopped fiber web ormesh. In the above described embodiments, the lightweight fillermaterial may disperse homogenously or uniformly throughout the fabric,mat, web, or mesh.

In other embodiments, the lightweight filler material may form a layeratop the fabric, mat, web or mesh. For example, when the fibers arepositioned relatively tightly together, such as when the fibers aretightly woven, or tightly packed in a nonwoven configuration, the hollowglass microspheres may be filtered by the fibers and form a layer atopthe fabric, mat, web, or mesh. In such embodiments, a second fabric,mat, web, or mesh may be positioned atop hollow glass microspheres sothat the microspheres are sandwiched between opposing fabric, mat, web,or mesh layers. In other embodiments, a second fabric, mat, web, or meshis not positioned atop the layer of hollow glass microspheres so thatthe layer of glass microspheres remains exposed to the surroundingenvironment.

Because of the low melt viscosity of the reactive resin, completeimpregnation of both the hollow glass microspheres and the reinforcingfibers can be easily achieved in a short period of time, ensuring ahigh-speed manufacturing process. As such, the process described hereinhas significant advantages in both production efficiency and compositeproperties, as compared to conventional melt-impregnation processes inwhich highly viscous polymeric resin melts are used to impregnatereinforcing fibers and/or hollow glass microspheres.

The fiber reinforcement of the lightweight prepreg can include any ofthe fabric, web, mesh, or mat configurations described herein, includingfabrics of various types, sizes, and arrangements; nonwoven mats ofvarious types, sizes, and arrangements; fiber webs or meshes of varioustypes, sizes, and arrangements; or any combination thereof. The fabric,webs, meshes, or mats can include one or more uniform layers and/or oneor more layers of fabric, webs, meshes, or mats. The reinforcing fibersmay be selected from, but not limited to, to following fiber types:glass fibers, carbon fibers, basalt fibers, polymer fibers includingaramid, natural fibers including cellulosic fibers, and other inorganicfibers. The reinforcing fibers can be treated with coupling agents,which may improve interfacial bonding between fibers and thethermoplastic resin matrix. The reinforcing fibers can be continuousfibers, chopped fibers, or a combination of both.

As briefly described herein, the lightweight prepreg may have a lowerdensity than conventional thermoplastic prepreg. For example, thelightweight prepreg may have a density of between 1.0 and 1.7 g/cm³. Thelightweight prepreg may comprise: a) 30 to 80% by weight of fibrousmaterial; b) 20 to 70% by weight of thermoplastic polymer; and c) 1 to30% by weight of lightweight filler. In preferred embodiments, thelightweight prepreg may comprise: a) 50 to 70% by weight of fibrousmaterial; b) 30 to 50% by weight of thermoplastic polymer; and c) 2 to15% by weight of lightweight filler.

Additional Thermoplastic Prepreg Systems

Referring now to FIG. 5 , illustrated is a system that may be used toproduce thermoplastic prepregs that include a chopped fiber web or mesh.As described herein, the resulting thermoplastic prepregs are fullyimpregnated with a thermoplastic polymer. The system of FIG. 5 iscapable of producing the fully impregnated thermoplastic prepregs in acontinuous process, in which the chopped fiber web or mesh iscontinually or constantly in movement through the system.

As illustrated in FIG. 5 , the system may include two vessels or holdingtanks (i.e., 21 and 22). At least one of the holding tanks functions asa storage and delivery tank of a reactive resin, which is typically amonomer or oligomer that is polymerizable into a thermoplastic polymer.In some embodiments, the monomers or oligomers may include or consist oflactams, lactones, cyclic butylene terephthalate (CBT), methylmethacrylate, precursors of thermoplastic polyurethane, or mixturesthereof. The lactams may include or consist of caprolactam, laurolactam,or mixtures thereof. The holding tanks, 21 and 22, may be heated andpurged with nitrogen to ensure the removal of any moisture, which couldotherwise reduce the reactivity of the raw materials and consequentlyreduce the conversion of the resins to a polymer. As previouslydescribed, one of the holding tanks (e.g., holding tank 21) may containa mixture of a resin and a catalyst. In a specific embodiment, theholding tank (e.g., tank 21) may include caprolactam and a catalyst,such as sodium caprolactamate or any other catalyst. The other holdingtank (e.g., tank 22) may contain a mixture of the resin and anactivator. In a specific embodiment, the other holding tank (e.g., tank22) includes caprolactam and an activator, such as N,N′-hexane-1,6-diylbis(hexahydro-2-oxo-1H-azepine-1-carboxamide) or anyother activator. The holding tanks, 21 and 22, may be heated to atemperature that allows the reactants to melt, such as between about 70and 120° C. for the reactive resin that includes caprolactam. The moltenreactants (e.g., the resin and activator or catalyst) have a very lowviscosity, for example, lower than 10 mPa-s. The viscosity of moltenreactants can be measured according to the test method ISO 3104:1999. Asan example, molten caprolactam at the temperature of 80° C. has aviscosity of 8.5 mPa-s, as measured using ISO 3104:1999.

The reactants from the two holding tanks, 21 and 22, are typicallymetered into a static mixer or mixing head 25 that ensures the correctratio of the monomers and/or oligomers, activator, and catalyst isdelivered to the chopped fiber web or mesh. In one embodiment, themixtures from the two holding tanks, 21 and 22, may be provided to thestatic mixer in a 1/1 ratio. The mixtures from the two holding tanks, 21and 22, are thoroughly mixed in the static mixer 25 into a substantiallyhomogenous mixture. The static mixer 25 may be heated to a temperaturethat allows the reactants to remain in a liquid non-polymerized state,such as between about 70 and 120° C. for the reactive resin thatincludes caprolactam.

The system also includes a double belt mechanism that includes an upperbelt 32 and a lower belt 31. The upper belt 32 is positioned atop thelower belt 31 and the two belts are configured to compress or squeeze afiber mesh that is passed through the double belt mechanism. At least aportion of the double belt mechanism is positioned within a curing oven30. In some embodiments, the top belt 32 is fully enclosed within thecuring oven 30. The lower belt 31 has a longitudinal length that issubstantially longer than the upper belt 32 so that at least a portionof the lower belt 31 extends outward from the curing oven 30. Asillustrated, the lower belt 31 may extend outward from a front edge ofthe curing oven 30 by a length L₁, which is typically between 2 and 15feet and more commonly between 3 and 10 feet. In a specific embodiment,the extended length L₁ of the lower belt 31 is between 6 and 9 feet andmore specifically about 8 feet.

The lower belt 31 typically extends outward from the upper belt 32and/or curing oven 30 so that one or more of the components of thesystem may be positioned atop the lower belt 31. For example, a fiberchopper 27 is positioned above the lower belt 31. The fiber chopper 27is configured to cut fiber strands or rovings 26 into chopped fiberstrands C, which form the chopped fiber web or mesh. The fiber chopper27 is positioned above the lower belt 31 so that as the fibers strandsor rovings 26 are cut into the individual chopped fiber strands C, thechopped fiber strands C fall atop the lower belt 31 and form the fiberweb or mesh. The fiber strands or rovings may be provided via one ormore spools, 23 a-c, that may be positioned on a creel. The strand orroving that is provided by each spool, 23 a-c, may be similar in fibertype or size or may differ from the strand or roving provided by anotherspool. Thus, the chopped fiber web or mesh may be formed from the sametype of fiber strands or rovings 26 or may be formed from a variety ofdifferent fiber strands or rovings. For example, the chopped fiber webor mesh may include a combination of different sized fibers and/or acombination of different types of fibers. In some instances, two or moredifferent types of fiber strands or rovings, including but not limitedto glass fiber, carbon fiber, and aramid fiber, may be cut by the fiberchopper 27 simultaneously, forming hybrid fiber web or mesh.

In some embodiments, the fibers of the fiber strands or rovings 26 mayinclude a sizing composition having a coupling agent that promotesbonding between the chopped fibers and the thermoplastic polymer. Forexample, the sizing composition may include a coupling activator thatcovalently bonds the polymerization activator moiety to the choppedfibers. In such instances, the bond between the thermoplastic polymerand the chopped fibers may be significantly strengthened or enhanced. Ina specific embodiment, the fiber sizing contains a mixture of silanecoupling agents, polymeric film formers, and other additives that aredesigned to enhance the interfacial bonding between the chopped fibersand a polyamide-6 matrix. Specifically, a reactive silane may be usedthat allows some of the polymerization to be initiated directly from thechopped fiber surface, thus improving the coupling between thereinforcing fibers and the resin matrix to improve composite properties.

In other instances, the activator may be included on the surface of thefibers of the fiber strands or rovings 26 so that the chopped fiber webor mesh includes the activator. In such instances, only a single holdingtank (e.g., tank 21) that contains the resin and catalyst may be used inthe system, or a reduced amount of the activator may be mixed with theresin in the second holding tank (e.g., tank 22). In some embodiments,the two holding tanks, 21 and 22, may each include a different resinmaterial. For example, a first holding tank 21 may include caprolactamwhile the second holding tank 22 includes laurolactam. In suchinstances, a combination of two or more types of reactive monomersand/or oligomers may be applied to the chopped fiber web or mesh.

The system may include a drying mechanism 24 that is configured to drythe fiber strands or rovings 26 as the fiber strands or rovings 26 areunwound from the respective spools, 23 a-c, and before the fiber strandsor rovings 26 are cut via the fiber chopper 27. The drying mechanism 24may be a tubular heater through which the fiber strands or rovings 26are pulled. The system may include a single tubular heater through whichall the fiber strands or rovings 26 are pulled, or may include a tubularheater through which each fiber strand or roving is individually pulledas it is unwound from the respective spool, 23 a-c. The use of thedrying mechanism 24 reduces or eliminates residual moisture that may bepresent on the fiber strands or rovings 26. The drying mechanism 24 mayhave a drying temperature of between 100° C. and 200° C., and morecommonly between 100° C. and 150° C.

The fiber chopper 27 cuts the fiber strands or rovings 26 intoindividual chopped fiber strands C, which fall atop the lower belt 31and form the chopped fiber web or mesh. The individual chopped fiberstrands C are randomly oriented or arranged atop the lower belt 31 andform a fiber web or mesh having a thickness and/or density that dependson the speed of the lower belt 31, the chopping speed of the fiberchopper 27, the number and/or size of fiber strands or rovings 26, andthe like. The chopped fiber web or mesh is typically not subjected tochemical or mechanical bonding and thus, the chopped fiber web or meshis typically un-bonded or un-adhered. Specifically, prior to applicationof the reactive resin, the chopped fiber web or mesh typically does notinclude a binder that bonds or adheres the fiber mesh together and thechopped fiber web or mesh is typically not subjected to a mechanicalentangling process, such as mechanical needling.

The lower belt 31 carries or conveys the chopped fiber web or meshtoward other components of the system and/or toward an entrance to thecuring oven 30. The chopped fiber web or mesh may be subjected to adrying mechanism 28 that removes residual moisture from the choppedfiber web or mesh. The drying mechanism 28 may be positioned atop thelower belt 31 so that it is above the chopped fiber web or mesh. Thedrying mechanism 28 dries the chopped fiber web or mesh as the choppedfiber web or mesh is moved underneath the drying mechanism 28. Thedrying mechanism 28 may be an infrared heater that raises thetemperature of the chopped fiber web or mesh and thereby removes anyresidual adventitious moisture. One of the reasons for the extendedlength L₁ of the lower belt 31 is to ensure that the chopped fiber webor mesh may be sufficiently dried before the application of the reactiveresin and to ensure that the chopped fiber web or mesh may be subjectedto each of the components of the system. The drying mechanism 28 mayremove trace amounts of surface moisture from the chopped fiber web ormesh.

After the chopped fiber web or mesh is dried via the drying mechanism28, the reactive resin is applied to the chopped fiber web or mesh usinga resin application mechanism 33 that is positioned atop the lower belt31 and above or adjacent the chopped fiber web or mesh. The resinapplication mechanism 33 applies the reactive resin R, which istypically monomers and/or oligomers of the thermoplastic material, tothe chopped fiber web or mesh as the chopped fiber web or mesh is movedpast and typically underneath the resin application mechanism 33. Insome embodiments, the resin application mechanism 33 is a slot diehaving a narrow opening through which the reactive resin R flows, suchas an opening of about 1.0 mm or less. The reactive resin R is deliveredto the resin application mechanism 33 from the static mixer 25 viatubing 29, which may be heated to maintain a temperature of the reactiveresin. In some embodiments, the resin application mechanism 33 isconfigured to apply a lightweight filler material (e.g., hollow glassmicrospheres) to the chopped fiber web or mesh as the chopped fiber webor mesh is moved past and typically underneath the resin applicationmechanism 33. In such embodiments, the lightweight filler material isapplied to the chopped fiber web or mesh simultaneously with thereactive resin R. The lightweight filler material may be contained ineither or both holding tanks, 21 and 22, along with the reactive resin Ror other materials. The lightweight filler material may be filtered bythe chopped fiber web or mesh and form a layer atop the chopped fiberweb or mesh, or may be dispersed through the chopped fiber web or meshas illustrated herein.

The reactive resin R may be applied to the chopped fiber web or meshclose to the curing oven 30 in order to minimize exposure of thereactive resin to the surrounding air and environment. In someembodiments, the resin application mechanism 33 may be positioned within10 inches of an inlet of the curing oven 30 and more commonly within 5.0inches or even 1.0 inches of the curing oven's inlet. In otherembodiments, a distal or delivery end of the resin application mechanism33 may be positioned within a hood or cover of the curing oven 30 asillustrated in FIG. 5 . The resin application mechanism 33 may betemperature controlled within a desired temperature range, for examplebetween a temperature of 70° C. and 120° C. for the reactive resin thatincludes caprolactam. The resin application mechanism 33 may include athermocouple and heating cartridge or other heating component to ensurethat the resin application mechanism 33 remains within the desiredtemperature range.

As an alternative to the slot die, the resin application mechanism 33may also include a spray application, curtain coating, dip and squeezecoating, kiss roll application, doctor blade application, or even powdercoating of pre-ground solid resins in which the curing oven melts thereactive components.

As previously described, the liquid handling lines 29 between theholding tanks, the static mixer, and the resin application die aretypically insulated and/or heated to minimize heat loss as the resinmixtures flow through the handling lines. Controlling the temperature ofthe liquid materials ensures that the resin R does not solidify and/orprematurely react within the handling lines. The temperature of thereactive resin is also typically maintained within a desired temperaturerange in order to maintain the reactive resin in a liquid or moltenstate while preventing premature polymerization of the resin prior tothe curing of the material in the oven. Similarly, once the choppedfiber web or mesh is coated with the reactive resin R, the surroundingenvironment in the vicinity of the coated chopped fiber web or mesh istypically controlled to ensure that the reactive resin is not exposed toambient moisture in the environment. Exposure of the reactive resin R toambient moisture may reduce the conversion of the reactive resin, whichmay result in a degree of polymerization less than 90%.

As previously described, the surrounding environment may be controlledby housing or enclosing the system in a room or area in which theenvironment is maintained substantially moisture-free. Variousdehumidification techniques can also be used to remove moisture from theambient air in the room or area. Exemplary dehumidification techniquesinclude desiccant dehumidification, refrigerant dehumidification, andelectrostatic dehumidification. More commonly, the system employs amoisture purge mechanism that is operable to ensure that the humidity inthe air surrounding the coated chopped fiber web or mesh issubstantially zero. For example, the system may employ a moisture purgemechanism that is operable to maintain the relatively humidity in theair surrounding the coated chopped fiber web or mesh to be below 1%.Typically the moisture purge mechanism need only be employed in thevicinity of the resin application mechanism 33 since the chopped fiberweb or mesh is free of the reactive resin R prior to the resinapplication mechanism 33. The moisture purge mechanism may be positionedproximally of the resin application mechanism 33 or distally of theresin application mechanism 33 as desired. In either instance, however,the moisture purge mechanism should be positioned relatively close tothe resin application mechanism 33 to minimize exposure of the reactiveresin to the surrounding air.

As illustrates in FIG. 5 , the moisture purge mechanism includes anair/gas plenum or tube 34 that blows a moisture-free gas G onto thechopped fiber web or mesh. The air/gas plenum or tube 34 is positionedatop the lower belt 31 and atop the chopped fiber web or mesh. Theair/gas plenum or tube 34 may be positioned directly adjacent the resinapplication mechanism 33 as illustrated in FIG. 5 so that themoisture-free gas G is blown directly onto the chopped fiber web or meshas the chopped fiber web or mesh is coated with the reactive resin R,and/or lightweight filler material, from the resin application mechanism33. In a specific embodiment, the air/gas plenum or tube 34 blows drynitrogen onto the chopped fiber web or mesh. The air/gas plenum or tube34 ensures that the area or vicinity around or adjacent the coatedchopped fiber web or mesh and/or in the vicinity of the curing oven'sinlet is kept substantially free of moisture.

After the chopped fiber web or mesh is coated with the reactive resin R,lightweight filler material, and/or the purge gas G is applied to thecoated chopped fiber web or mesh, the coated chopped fiber web or meshis then subjected to a press mechanism that facilitates in a completewet-out of the chopped fibers by the reactive resin. The press mechanismfunction is typically performed by the upper belt 32 and the lower belt31, which form a double belt compression mechanism. As illustrated inFIG. 5 , a distal end of the upper belt 32 may be positioned proximallyof the curing oven's inlet by a distance L₂, which distance may ensuresufficient room for the distal end of the resin application mechanism 33and air/gas plenum or tube 34 to be positioned within the curing oven 30between the upper belt 32 and curing oven inlet. The distance L₂ may bebetween 0.2 and 2.0 feet and more commonly between 0.5 and 1.0 feet. Theupper belt 32 and lower belt 31 compress the coated chopped fiber web ormesh as the fiber web or mesh is passed through the curing oven 30. Thecompression of the coated chopped fiber web or mesh facilitates in thereactive resin (e.g., monomers and/or oligomers) fully saturating thechopped fiber web or mesh. Fully saturating the chopped fiber web ormesh means that the reactive resin completely impregnates individualchopped fiber strands of the web or mesh. The compression of the coatedchopped fiber web or mesh between the upper belt 32 and lower belt 31also minimizes exposure of the coated chopped fiber web or mesh toambient moisture in the surrounding environment. In some embodiments,the pressing function may be achieved by one or more calendars orrollers that press or squeeze the reactive resin through the choppedfiber web or mesh.

The lower and upper belts, 31 and 32, pass the coated chopped fiber webor mesh through the curing oven 30. The temperature of the curing oven30 is maintained at a temperature that ensures complete polymerizationof the reactive resin. Stated differently, the curing oven 30 ismaintained at a polymerization temperature at which the monomers and/oroligomers start to polymerize, which is typically about 100° C. or more.For a reactive resin composition that includes caprolactam, thepolymerization temperature may be about 120° C. or more (e.g., about120° C. to about 220°). For prepreg manufacturing processes where thepolymerized resin matrix is not melted, an upper limit on thepolymerization temperature for the monomers and/or oligomers may be themelting temperature of the polymer. For example, a reactive resincomposition that includes caprolactam may have a upper limit of apolymerization temperature that is the melting temperature of thepolyamide-6 (i.e., ˜220° C.). The coated chopped fiber web or mesh maybe exposed to the curing oven 30 for a time which is sufficient toensure complete polymerization of the reactive resin material. Forexample, for a reactive resin composition that includes caprolactam, theresidence time of the coated chopped fiber web or mesh in the curingoven may be about 3 minutes to ensure the complete polymerization ofcaprolactam. Upon polymerization of the reactive resin, the choppedfiber web or mesh is fully impregnated with the thermoplastic polymer.As used herein, the description of the chopped fiber web or mesh beingfully impregnated with the thermoplastic polymer means that thethermoplastic polymer impregnates the chopped fiber web or mesh to adegree such that the chopped fiber web or mesh has a void content of thecomposites of less than 3% in volume based on the total volume of thethermoplastic prepreg. In some embodiments, the chopped fiber web ormesh may have a void content of the composites of less than 1% in volumebased on the total volume of the thermoplastic prepreg. Void content ofthe resulting prepregs can be measured according to the test method ASTMD2734-16.

In some instances the system may be configured to ensure that theviscosity of the reactive resin R remains low before the chopped fiberweb or mesh is fully impregnated with the reactive resin. Specifically,the polymerization of the reactive resin R may be controlled to ensurethat the chopped fiber web or mesh is fully saturated with the resinbefore the resin polymerizes.

In some embodiments, a distal end of the oven or enclosure 30 includes acooling mechanism 35 that is configured to cool a fully cured choppedfiber thermoplastic prepreg 36. The cooling mechanism 35 may cool thechopped fiber thermoplastic prepreg 36 in order to allow the choppedfiber thermoplastic prepreg 36 to be cut to shape, to be handled by anindividual, to reduce or prevent warpage of the chopped fiberthermoplastic prepreg 36, or for any other reason. The cooling mechanism35 typically cools the chopped fiber thermoplastic prepreg 36 to below50° C. and more commonly to at or near ambient temperature, which allowsthe chopped fiber thermoplastic prepreg 36 to be handled by anindividual without burning or harming the individual. The coolingmechanism 35 may include chilled water cooling.

Upon exiting the curing oven 30, a fully cured chopped fiberthermoplastic prepreg 36 is formed or produced. The system may include acutting mechanism 38 that is configured to cut the fully cured choppedfiber thermoplastic prepreg into sheets, which may be stacked atop oneanother. In other embodiments, the system may include a windingmechanism that is configured to wind the fully cured chopped fiberthermoplastic prepreg into a roll product. The system of FIG. 5 isdesigned so that the process is performed in a time of 20 minutes orless, and more commonly 10 minutes or less. In some embodiments, theprocess may be performed in 5 minutes or less. The speed and efficiencyof the system is not drastically affected when multiple layers of fibermaterial are employed, such as in the systems of FIGS. 6-8 . Rather, thelow viscosity reactive resin is able to easily penetrate through andsaturate the multiple layers of fiber material so that the overallprocessing time remains low and relatively unaffected. Full impregnationof the stacked layers is also achievable due to the low viscosity of theresin materials.

Although the lower belt 31 is illustrated as extending from the inlet ofthe curing oven 30, in some embodiments the lower belt 31 may be fullyenclosed within the curing oven 30, or within a hood or cover of thecuring oven. In such embodiments, the lower belt 31 extends beyond thedistal or front edge of the upper belt 32 so that the other componentsof the system (i.e., the fiber chopper 27, filler material applicationmechanism 60, fiber scattering unit 37, drying mechanism 28, resinapplication mechanism 33, etc.) are able to remain positioned above thelower belt 31. In such an embodiment, the other components of the systemare typically enclosed within curing oven 30, or within a hood or coverof the curing oven 30.

FIG. 6 illustrates a similar system except that the system includesmultiple fiber choppers. Specifically, the system includes a first fiberchopper 27 a and a second fiber chopper 27 b that are each positionedatop the lower belt 31 and configured to cut fiber strands or rovings.The first fiber chopper 27 a cuts first fiber strands or rovings 26 athat are unwound from the respective spools, 23 a-c. The chopped firstfiber strands or rovings 26 a fall atop the lower belt 31 and form afirst layer of a chopped fiber web or mesh. The first strands or rovings26 a may pass through a first roving heater 24 a that dries the firststrands or rovings 26 a. The thickness and/or density of the first layeris controlled by the speed of the first fiber chopped 27 a, the numberand sizes of individual rovings in 26 a, and the speed of the lower belt31. The second fiber chopper 27 b cuts second fiber strands or rovings26 b that are unwound from the respective spools, 23 d-f. The choppedsecond fiber strands or rovings 26 b fall atop the lower belt 31 and/orthe first layer and form a second layer of the chopped fiber web ormesh. The second strands or rovings 26 b may pass through a secondroving heater 24 b that dries the second strands or rovings 26 b. Thethickness and/or density of the second layer is controlled by the speedof the second fiber chopped 27 b, the number and sizes of individualrovings in 26 b, and the speed of the lower belt 31.

The resulting chopped fiber web or mesh may have a layered configurationin which at least one property of the first layer is different than aproperty of the second layer. The properties may differ in fiber type,fiber length, fiber diameter, fiber or layer density, layer thickness,and the like. In some embodiments, the first and second strands orrovings, 26 a and 26 b, may be different fiber types, different fibersizes, and/or have different fiber characteristics. In otherembodiments, the chopped fibers that are produced by the first fiberchopper 27 a and the second fiber chopper 27 b may fall atop the lowerbelt 31 so that a hybrid layer is formed of the chopped fibers. Thehybrid layer may include a mixture of the chopped fibers from the firstand second fiber choppers, 27 a and 27 b. The multiple fiber choppersmay be used simply to cut strands or rovings that have differentproperties. The layered or hybrid chopped fiber web or mesh may then besubjected to the other processes of the system, such as the dryingmechanism 28, resin application mechanism 33, gas purge mechanism 34,double belt compression mechanism, curing oven 30, and the like. Theresin application mechanism 33 may apply a reactive resin R and/or alightweight filler material to the layered or hybrid chopped fiber webor mesh. In some embodiments, the first and second roving heaters, 24 aand 24 b, may be the same heater. The system may also include additionalfiber choppers (not shown) that cut additional fiber strands or rovingsto form additional layers of the chopped fiber web or mesh as desired.

FIG. 7 illustrates a hybrid system in which the thermoplastic prepreg isformed of both the chopped fiber web or mesh and a woven/nonwoven fibermat, web, or fabric. The system includes an unwinder 41 about which afiber mat, web, or fabric 40 is positioned. The system is configured tounwind the fiber mat, web, or fabric 40 from the unwinder and to movethe fiber mat, web, or fabric 40 atop the lower belt 31. The fiberchopper 27 is positioned above the lower belt 31 and the fiber mat, web,or fabric 40 so that the chopped fibers C fall atop the fiber mat, web,or fabric 40 and typically form a chopped fiber web or mesh layer atopthe fiber mat, web, or fabric 40. The thickness of the chopped fiber webor mesh may be controlled by controlling a speed of the fiber chopped27, and/or a speed of the lower belt 31.

In some embodiments the chopped fibers C may fall within the fiber mat,web, or fabric 40 to form a hybrid layer that consists of the fiber mat,web, or fabric 40 and the chopped fiber web or mesh. In suchembodiments, the fiber mat, web, or fabric 40 must be porous enough toenable the chopped fibers C to fall within and through the fiber mat,web, or fabric 40. The fibers or strands 26 may be cut in sufficientsmall pieces to facilitate dispersion of the chopped fibers C within thefiber mat, web, or fabric 40.

The resulting layered or hybrid mat is then moved past the dryingmechanism 28 to remove residual moisture from the layered or hybrid mat.The layered or hybrid mat is then moved past the resin applicationmechanism 33 so that the reactive resin R, and in some embodiments thelightweight filler material, is applied to the mat and is moved past thegas purge mechanism 34 so that the moisture free gas G is applied to thelayered or hybrid mat. The layered or hybrid mat is then moved throughthe double belt mechanism to fully saturate the layered or hybrid matand moved through the curing oven 30 to polymerize the reactive resin.Upon polymerization of the reactive resin, the thermoplastic polymerfully impregnates the layered or hybrid mat.

The layered or hybrid mat may provide several advantages overthermoplastic prepregs that employ only a woven/nonwoven fiber mat, web,or fabric. In particular, the layered or hybrid mat may have improvedconformability. The improved conformability of the thermoplastic prepregallows the prepreg to more easily conform to molds having complexshapes. Thus, it is easier to form the prepreg into complex shapes. Theuse of the fiber mat, web, or fabric typically provides improvedstrength over prepregs that merely employ chopped fiber webs or meshes.

FIG. 8 illustrates another hybrid system in which multiple fiberchoppers and a single fiber mat, web, or fabric is employed. It shouldbe realized that the configuration of the system of FIG. 8 may bereversed so that multiple fabrics or mats and a single fiber chopper isemployed. Alternatively, the system of FIG. 8 may use both multiplefabrics or mats and multiple fiber choppers if desired to form athermoplastic prepreg having a desired chopped fiber web or mesh andfiber mat, web, or fabric configuration.

In FIG. 8 , a first fiber chopper 27 a is positioned atop a distal endof the lower belt 31. The first fiber chopper 27 a cuts first fiberstrands or rovings 26 a that are unwound from about respective spools,23 a-c. The chopped first fiber strands or rovings 26 a fall atop thelower belt 31 and form a first layer of a chopped fiber web or mesh. Thefirst strands or rovings 26 a may pass through a first roving heater 24a that dries the first strands or rovings 26 a. The thickness and/ordensity of the first layer is controlled by the speed of the first fiberchopped 27 a the number and sizes of individual rovings in 26 a, and thespeed of the lower belt 31. The system also includes an unwinder 41about which a fiber mat, web, or fabric 40 is positioned. The fiber mat,web, or fabric 40 is unwound from the unwinder 41 and is moved atop thechopped fiber web or mesh formed by the first chopped fiber strands orrovings 26 a. A roller 42 may be positioned above the lower belt 31 toproperly direct the fiber mat, web, or fabric 40 onto and atop thechopped fiber web or mesh. A second fiber chopper 27 b is positionedproximally of the fiber mat, web, or fabric roller 41 and is configuredto cuts second fiber strands or rovings 26 b that are unwound from aboutrespective spools, 23 d-f. The chopped second fiber strands or rovings26 b fall atop the fiber mat, web, or fabric 40 and form a second layerof the chopped fiber web or mesh atop the fiber mat, web, or fabric 40.The second strands or rovings 26 b may pass through a second rovingheater 24 b that dries the second strands or rovings 26 b. The thicknessand/or density of the second layer is controlled by the speed of thesecond fiber chopped 27 b, the number and sizes of individual rovings in26 b, and the speed of the lower belt 31. The fiber mat, web, or fabric40 is thus sandwiched between two layers of chopped fiber webs ormeshes. The fiber mat, web, or fabric and chopped fiber webs or meshesare then moved through the system to remove residual moisture, apply thereactive resin, and polymerize the reactive resin. The resulting hybridthermoplastic prepreg 36 may then be rolled about a roller or beam 38 toform a roll product as described herein.

FIG. 8A illustrates a hybrid system in which the fiber chopper isreplaced with a fiber scattering unit 37. The fiber scattering unit 37is configured to scatter or disperse pre-cut chopped fiber segments Cthat are loaded or positioned within a hopper. In some embodiments, thechopped fiber segments C are scattered uniformly atop the lower belt 31to form a chopped fiber web or mesh. In such embodiments, the system ofFIG. 8A does not include the fiber mat, web, or fabric roller 41 andfiber mat, web, or fabric 40. In other embodiments, the chopped fibersegments C are uniformly scattered atop a fiber mat, web, or fabric 40to form a layer of the chopped fiber web or mesh atop the fiber mat,web, or fabric 40. The system of FIG. 8A may include an additional fiberscattering unit 37 and/or fiber chopper to form additional fiber web ormesh layers and/or to disperse different fiber sizes or types within thefiber web or mesh. The chopped fibers C may be fully dried prior toscattering or dispersing them atop the lower belt 31 or fiber mat, web,or fabric 40. The system may include the various other componentsdescribed herein, or may exclude one or more of those components asdesired. In some embodiments, the lightweight filler material may becombined with chopped fibers in the hopper. In such embodiments, thefiber scatter unit 37 may be configured to disperse or scatter both thechopped fibers and lightweight filler material atop the lower belt 31 orfiber mat, web, or fabric 40. The chopped fibers and lightweight fillermaterial may be dispersed uniformly atop the lower belt 31 or fiber mat,web, or fabric 40.

FIG. 8B illustrates a hybrid system in which the fully cured choppedfiber thermoplastic prepreg 36 is wound into a roll product via awinding mechanism 39. The thermoplastic prepreg may be formed solely ofa chopped fiber web or mesh or may be formed of both the chopped fiberweb or mesh and a woven/nonwoven fiber mat, web, or fabric. When thethermoplastic prepreg is formed of the chopped fiber web or mesh andwoven/nonwoven fiber mat, web, or fabric, the system includes anunwinder 41 about which a fiber mat, web, or fabric 40 is positioned aspreviously described. The system of FIG. 8B may include one or morefiber choppers C and/or rollers 41 to form any type of layered prepregthat is desired.

FIG. 9 illustrates a system that includes a filler material applicationmechanism 60 that is positioned atop the lower belt 31 and typicallybefore the drying mechanism 28. The filler material applicationmechanism 60 is configured to apply a light weight filler material to aweb or mesh of chopped fibers that are supplied via a fiber chopper 27or a fiber scattering unit 37. In some embodiments, the filler materialapplication mechanism 60 may be positioned immediately adjacent to thefiber chopper 27 and/or fiber scattering mechanism 37 so that thelightweight filler material is added atop the lower belt 31 nearlysimultaneously with the chopped fibers. In such embodiments, thelightweight filler material may be essentially homogenously dispersedwithin the chopped fiber web or mesh. In other embodiments, the fillermaterial application mechanism 60 may be positioned downstream of thefiber chopper 27 and/or fiber scattering mechanism 37 so that thelightweight filler material is added atop the chopped fiber web or meshto form a layer of the lightweight filler material atop the choppedfiber web or mesh. The filler material application mechanism 60 may be apowder applicator or device that is configured to apply light weightfiller material (e.g., hollow glass microspheres) to the fiber web ormesh. The filler material application mechanism 60 may be adjustable tovary a speed with which the light weight filler material is applied. Theapplication speed of the lightweight filler material may be varied tochange the thickness of the lightweight filler material layer and/or toaccommodate the speed of the lower belt 31 and/or fiber chopper 27 orfiber scattering unit 37. In some embodiments, the lightweight fillermaterial (e.g., hollow glass microspheres) includes a sizing compositionhaving a coupling agent that promotes bonding between the lightweightfiller material and the thermoplastic polymer material.

The system of FIG. 9 may include an additional fiber chopper 27, fiberscattering unit 37, and/or filler material application mechanism 60 toform additional lightweight filler material and/or fiber web or meshlayers as desired. The drying mechanism 28 may be configured to removeresidual moisture from the chopped fiber web or mesh and the lightweightfiller material as these materials or layers are moved past the dryingmechanism. In other embodiments, the lightweight filler material may bedried via a separate drying mechanism (not shown) prior to being appliedatop or with the chopped fiber web or mesh. In such embodiments, thedrying mechanism 28 may be employed mainly to dry the chopped fiber webor mesh.

In some embodiments, additional lightweight filler materials may beprovided via the fiber scattering unit 37 and/or resin applicationmechanism 33 as described herein to form a thermoplastic prepreg with ahigh filler content. The chopped fiber web or mesh and filler materialmay be subjected to the other processes of the system, such as the gaspurge mechanism 34, double belt compression mechanism, curing oven 30,cutting mechanism 38, roll mechanism 39, and the like.

FIG. 10 illustrates a system that includes a filler material applicationmechanism 60 that is positioned atop the lower belt 31 and that isconfigured to apply a light weight filler material to a fiber mat, web,or fabric 40 that is unrolled from an unwinder 41. The filler materialapplication mechanism 60 typically adds the lightweight filler materialatop the fiber mat, web, or fabric 40 so that a layer of the lightweightfiller material is formed atop the fiber mat, web, or fabric 40. In someembodiments, the lightweight filler material may penetrate into thefiber mat, web, or fabric 40, such as when the fiber mat, web, or fabric40 has a relatively loose fiber weave or loose fiber nonwovenconfiguration. In such embodiments, the lightweight filler material isdisposed at least partially within the fiber mat, web, or fabric 40. Adegree of penetration of the lightweight filler material into the fibermat, web, or fabric 40 can be controlled by controlling the tightness ofthe fiber weave or a porosity of the nonwoven fiber mat. In someembodiments, the lightweight filler material may penetrate through thefiber mat, web, or fabric 40. As previously described, the fillermaterial application mechanism 60 may be a powder applicator or devicethat is configured to apply lightweight filler material (e.g., hollowglass microspheres) to the fiber mat, web, or fabric. In someembodiments, the lightweight filler material (e.g., hollow glassmicrospheres) includes a sizing composition having a coupling agent thatpromotes bonding between the lightweight filler material and thethermoplastic polymer material.

The drying mechanism 28 may be configured to remove residual moisturefrom the fiber mat, web, or fabric 40 and the lightweight fillermaterial as these materials or layers are moved past the dryingmechanism. In other embodiments, the lightweight filler material may bedried via a separate drying mechanism (not shown) prior to being appliedatop the fiber mat, web, or fabric 40. In such embodiments, the dryingmechanism 28 may be employed mainly to dry the fiber mat, web, or fabric40. In some embodiments, additional lightweight filler materials may beprovided via the resin application mechanism 33 as described herein toform a thermoplastic prepreg with a high filler content. The fiber mat,web, or fabric 40 and filler material may be subjected to the otherprocesses of the system, such as the gas purge mechanism 34, double beltcompression mechanism, curing oven 30, cutting mechanism 38, rollmechanism 39, and the like.

FIG. 11 illustrates a system that includes a filler material applicationmechanism 60 that is positioned atop the lower belt 31 and that isconfigured to apply a light weight filler material to a fiber mat, web,or fabric 40 and a chopped fiber web or mesh. The system includes anunwinder 41 that provides the fiber mat, web, or fabric 40 and includesa fiber chopper 27 and/or a fiber scattering unit 37 that provideschopped fibers C. FIG. 11 illustrates the filler material applicationmechanism 60 being positioned between the unwinder 41 and the fabricchopper 27/fiber scattering unit 37. It should be realized, however,that the filler material application mechanism 60 may be positionedelsewhere as desired, such as after both the unwinder 41 and the fabricchopper 27/fiber scattering unit 37. Additionally, the position of theunwinder 41 and the fabric chopper 27/fiber scattering unit 37 may beswitched in the system of FIG. 11 as desired. It should also be realizedthat the system may include additional unwinders 41, filler materialapplication mechanisms 60, and/or fabric choppers 27/fiber scatteringunits 37 as desired to form a thermoplastic prepreg having any desiredconfiguration.

The lightweight filler material may penetrate into the fiber mat, web,or fabric 40 and/or chopped fiber web or mesh so that the lightweightfiller material is disposed at least partially within the fiber mat,web, or fabric 40 and/or chopped fiber web or mesh. A degree ofpenetration of the lightweight filler material into the fiber mat, web,or fabric 40 and/or chopped fiber web or mesh can be controlled bycontrolling the tightness of the fiber weave, a porosity of a nonwovenfiber mat, or a looseness of the chopped fibers. The lightweight fillermaterial more commonly forms a layer that is positioned between thefiber mat, web, or fabric 40 and chopped fiber web or mesh or atop boththe fiber mat, web, or fabric 40 and the chopped fiber web or mesh.

The drying mechanism 28 may be configured to remove residual moisturefrom the fiber mat, web, or fabric 40, the chopped fiber web or mesh,and the lightweight filler material as these materials or layers aremoved past the drying mechanism. In some embodiments, the lightweightfiller material may be dried via a separate drying mechanism (not shown)prior to being applied atop the fiber mat, web, or fabric 40. In suchembodiments, the drying mechanism 28 may be employed mainly to dry thechopped fiber web or mesh and/or fiber mat, web, or fabric 40. In someembodiments, additional lightweight filler materials may be provided viathe resin application mechanism 33 and/or fiber scattering unit 37 asdescribed herein to form a thermoplastic prepreg with a high fillercontent. The fiber mat, web, or fabric 40 and filler material may besubjected to the other processes of the system, such as the gas purgemechanism 34, double belt compression mechanism, curing oven 30, cuttingmechanism 38, roll mechanism 39, and the like.

Exemplary Prepregs

The above system may be used to manufacture a fully impregnatedthermoplastic prepreg. The thermoplastic prepreg may include a fibermat, web, or fabric, a chopped fiber web or mesh, or a hybrid web ormat. In one embodiment, the fiber mat, web, or fabric may include aplurality of rovings that are woven together. Each roving may contain abundle of continuous glass fibers or any other fibers. In anotherembodiment, the fiber mat, web, or fabric may include a plurality ofentangled and intermeshed fibers that are randomly oriented. In yetanother embodiment, a web or mesh of un-bonded chopped fibers may beemployed. The prepreg also includes a thermoplastic polymer that isfully impregnated within the fiber mat, web, or fabric, chopped fiberweb or mesh, or hybrid web or mat. The thermoplastic polymer is formedby polymerizing a reactive resin (e.g., caprolactam, CBT, and the like)to form the thermoplastic polymer (e.g., polyamide-6, PBT, and thelike). As described herein, greater than 90%, 95%, 98%, or even 99% byweight of the resin reacts to form the thermoplastic polymer. When thefully impregnated thermoplastic prepreg is subjected to a subsequentheating and/or pressure process, the thermoplastic polymer melts orsoftens to allow the thermoplastic prepreg to be molded or formed into acomposite part.

In some embodiments, the fully impregnated thermoplastic prepreg is arolled product. In some other embodiments, the fully impregnatedthermoplastic prepreg may be cut to sheets. The thermoplastic prepregmay be subsequently formed into a composite part. For example, one ormore layers of the thermoplastic prepreg may be compression molded intoa desired composite part. Exemplary techniques for forming the prepregsinto the fiber-reinforced composite articles may include compressionmolding of a single prepreg layer, multiple prepreg layers, and/orpellets of prepreg material into the fiber-reinforced article. When theprepreg includes partially-polymerized resin, the compression moldingprocess may include a heating step (e.g., hot pressing) to fullypolymerize the resin. Heat may also be used in the compression moldingof fully-polymerized prepregs to melt and mold the prepreg into theshape of the final article.

The prepregs may also be used to in conjunction with other fibers andresin materials to make the final composite article. For example, theprepreg may be placed in selected sections of a tool or mold toreinforce the article and/or provide material in places that aredifficult to reach for thermoset and/or thermoplastic resins. Forexample, the prepregs may be applied to sharp corners and other highlystructured areas of a mold or layup used in reactive injection moldingprocesses (RIM), structural reactive injective molding processes (SRIM),resin transfer molding processes (RTM), vacuum-assisted resin transfermolding processes (VARTM), spray-up forming processes, filament windingprocesses, and long-fiber injection molding processes, among others. Theprepreg may also be used as local reinforcement or for overmoldingduring injection and compression molding processes including LFT (longfiber thermoplastic) and D-LFT (direct-long fiber thermoplastic).

Exemplary composite products that may be formed from the prepregsinclude: automotive components, wind turbine blade components, buildingand construction components, electrical components, sports and leisurecomponents, and/or other components. Exemplary automotive componentsinclude: cockpit, seats, instrument panels, side beams, bottom plate,bottom plate side beam, door trims, body panels, openings, underbody,front/rear modules, engine compartment, engine covers, battery trays,oil pans, bonnets/hoods, fenders, spoilers, and the like.

Exemplary wind turbine blade components include: spar cap, shells, rootinserts, and the like. Exemplary building and construction componentsinclude: columns, pediments, domes, panels, window profiles, ladderrails, and the like. Exemplary electrical components include: lightpoles, circuit boards, electrical junction boxes, and the like.Exemplary sports and leisure components include: golf club shafts, golftrolleys, and the like. Other components that may be formed form theprepregs include: components for mass transportation, agriculturalequipment, and trailers/RV including passenger seats, standbacks, wallcladdings, floor panels, large panels for trailer walls, truck andtractor cabs, bus body shells, cargo containers, and the like.

In a specific embodiment, a battery tray or compartment for an electriccar or vehicle may be molded using the fully impregnated thermoplasticprepregs described herein. The battery compartment may be molded from asingle piece of the prepreg material, thereby eliminating the need touse unidirectional tape on the corners or edges to reinforce these areasof the battery compartment, as is done in conventional processes.

Referring to FIG. 12 , illustrated is a thermoplastic prepreg that maybe formed by one of the systems and/or methods described herein. Thethermoplastic prepreg includes a web or mesh of fibers 50 that includesa plurality of chopped fibers 51 having a fiber length and a fiberdiameter. The fiber length is typically between 10 and 100 mm and morecommonly between 25 and 50 mm. The fiber diameter is typically between 1and 30 μm and more commonly between 5 and 20 μm. As described herein,the web or mesh of fibers 50 is typically un-bonded prior to theapplication of a reactive resin and thus, the web or mesh of fibers 50is typically not mechanically bonded and does not include a binder otherthan the thermoplastic material that binds the chopped fibers together.The web or mesh of fibers 50 is also not typically coupled together viasome means other than the thermoplastic material. The web or mesh offibers 50 may include multiple fiber types and/or fiber sizes asdescribed herein that are homogenously or uniformly dispersed within theweb or mesh of fibers 50 and that form a hybrid fiber mesh. The choppedfibers 51 may include a sizing composition that has a coupling agentthat promotes bonding between the chopped fibers 51 and thethermoplastic polymer. The chopped fibers may include or consist ofglass fibers, carbon fibers, basalt fibers, metal fibers, ceramic fiber,natural fibers, synthetic organic fibers, aramid fibers, inorganicfibers, or combinations thereof. In some instances, it may be beneficialto use a chemically or mechanically coupled web or mesh of fibers 50 andthus, the web or mesh of fibers 50 is not limited to a specificconfiguration (i.e., bonded or un-bonded) unless specifically recited inthe claims.

The thermoplastic material fully impregnates the web or mesh of fibers50 so that the thermoplastic prepreg has a void content of less than 5%and more commonly less than 3%. In most embodiments, the thermoplasticprepreg has a void content of less than 3% and sometime less than 1%. Asdescribed herein, the thermoplastic material comprises or consists ofpolymers that are formed by in-situ polymerization of monomers oroligomers in which greater than 90%, 95%, 98%, or even 99% by weight ofthe monomers or oligomers react to form the thermoplastic material. Thethermoplastic prepreg includes 5 to 95 weight percent of thethermoplastic material. The thermoplastic material may include orconsist of nylon, PMMA, PBT, thermoplastic polyurethane (TPU), ormixtures thereof.

FIG. 13 illustrates another thermoplastic prepreg in which the web ormesh of fibers includes a first layer 50 a of fibers formed of firstchopped fibers 51 a and a second layer 50 b of fibers formed of secondchopped fibers 51 b. The first chopped fibers 51 a and second choppedfibers 51 b are typically different fiber types and/or fiber sizes. Thecomposition of each fiber layer, the density of each fiber layer, and/orthe thickness of each fiber layer may be selected based on a givenapplication for the thermoplastic prepreg and/or based on a desiredprepreg property. The first chopped fibers 51 a and second choppedfibers 51 b are typically not entangled or intermixed except for at aninterface between the first layer 50 a and the second layer 50 b. Thethermoplastic material fully impregnates the fiber web or mesh. Thethermoplastic prepreg may have a void content and polymerizationpercentage as described herein. The thermoplastic prepreg of FIG. 13 maybe formed via the system illustrated in FIG. 6 .

FIG. 14 illustrates a thermoplastic prepreg that has a layeredconfiguration in which each layer includes a different fiberreinforcement. Specifically a first layer of the thermoplastic prepregincludes the web or mesh of chopped fibers 50 and a second layer of thethermoplastic prepreg includes a woven fabric or nonwoven mat 52. Asdescribed herein the woven fabric or nonwoven mat 52 is typically formedof continuous fiber strands or a plurality of entangled or bonded fibersegments. The composition of each layer, the density of each layer,and/or the thickness of each layer may be selected based on a givenapplication for the thermoplastic prepreg and/or based on a desiredprepreg property. The thermoplastic material fully impregnates the fiberreinforcement. The thermoplastic prepreg may have a void content andpolymerization percentage as described herein. The thermoplastic prepregof FIG. 14 may be formed via the system illustrated in FIG. 7 .

FIG. 15 illustrates a thermoplastic prepreg that has a layeredconfiguration in which the woven fabric or nonwoven mat 52 is sandwichedbetween an upper layer of the web or mesh of chopped fibers 50 and alower layer of a web or mesh of chopped fibers 53. The composition ofeach layer, the density of each layer, and/or the thickness of eachlayer may be selected based on a given application for the thermoplasticprepreg and/or based on a desired prepreg property. The thermoplasticmaterial fully impregnates the fiber reinforcement. The thermoplasticprepreg may have a void content and polymerization percentage asdescribed herein. The thermoplastic prepreg of FIG. 15 may be formed viathe system illustrated in FIG. 8 .

FIG. 16 illustrates a thermoplastic prepreg that also has a layeredconfiguration, but is opposite the configuration of FIG. 15 in that theweb or mesh of chopped fibers 50 is sandwiched between an upper layer ofthe woven fabric or nonwoven mat 52 and a lower layer of a woven fabricor nonwoven mat 54. The composition of each layer, the density of eachlayer, and/or the thickness of each layer may be selected based on agiven application for the thermoplastic prepreg and/or based on adesired prepreg property. The thermoplastic material fully impregnatesthe fiber reinforcement. The thermoplastic prepreg may have a voidcontent and polymerization percentage as described herein. Thethermoplastic prepreg of FIG. 16 may be formed via a system similar tothat illustrated in FIG. 8 in which a single fiber chopper is employedand two fabrics or mats are employed. Alternatively, a thermoplasticprepreg(s) formed via the system of FIG. 1A or 1B may bethermoplastically bonded with a thermoplastic prepreg formed via any ofthe systems of FIGS. 5-7 .

Referring to FIG. 17 , illustrated is a lightweight thermoplasticprepreg that may be formed by one of the systems and/or methodsdescribed herein, and in particular, the systems of FIGS. 9-11 . Thethermoplastic prepreg includes a mat or web 80 that includes a pluralityof fibers 82 having a fiber length and a fiber diameter. The fibers 82may be chopped fibers, nonwoven fibers, or continuous fibers that aretypically used in woven fabrics so that the mat or web 80 is a wovenfabric, a nonwoven mat, a chopped fiber mesh, or any combinationthereof. The mat or web 80 also includes a light weight filler material,which in an exemplary embodiment is hollow glass microspheres 84. Thelightweight filler material will be referred to in relation to FIGS.17-19 as hollow glass microspheres 84, although it should be realizedthat the lightweight material may also be perlite or some otherlightweight material. The hollow glass microspheres 84 are homogenouslydispersed within the plurality of fibers of the mat or web 80.

A thermoplastic polymer is fully impregnated through the mat or web 80and the hollow glass microspheres 84. The thermoplastic polymerimpregnates the mat or web 80 such that the thermoplastic prepreg issubstantially free of gaps or voids. The thermoplastic material is madeof polymerized monomers and oligomers in which greater than 90% of themonomers or oligomers react to form the thermoplastic material.

The mat or web 80 may include multiple fiber types and/or fiber sizes asdescribed herein that are homogenously or uniformly dispersed within themat or web 80. The hollow glass microspheres 84 and/or the fibers 82 ofthe mat or web 80 may include a sizing composition having a couplingagent that promotes bonding between the hollow glass microspheres or thefibers and the thermoplastic polymer. The fiber 82 may include glassfibers, carbon fibers, basalt fibers, metal fibers, ceramic fiber,natural fibers, synthetic organic fibers, aramid fibers, inorganicfibers, or combinations thereof. The thermoplastic material may includenylon, PBT, PMMA, thermoplastic polyurethane, and combinations thereof.The lightweight thermoplastic prepreg may be formed or cut into sheetsor rolled into a roll product as desired.

The thermoplastic material fully impregnates the web or mesh of fibers50 so that the thermoplastic prepreg has a void content of less than 5%and more commonly less than 3%. In most embodiments, the thermoplasticprepreg has a void content of less than 1%. As described herein, thethermoplastic material comprises or consists of polymers that are formedby in-situ polymerization of monomers or oligomers in which greater than90%, 95%, 98%, or even 99% of the monomers or oligomers react to formthe thermoplastic material. The thermoplastic prepreg includes 5 to 95weight percent of the thermoplastic material. As described herein, aresidual amount of the monomer or oligomers may remain unpolymerized inthe lightweight thermoplastic prepreg. The residual monomer or oligomercontent can be measured via the solvent extraction method describedherein.

Referring not to FIG. 18 , illustrated is a lightweight prepreg having alayered configuration. Specifically, the lightweight prepreg includes afirst layer 90 that includes a mat, web, or mesh of fibers 82. The firstlayer 90 may include any of the fiber configurations or arrangementillustrated in FIGS. 12-16 , and in particular is typically a wovenfabric, nonwoven mat layer, chopped fiber mesh, or any combinationthereof. A second layer 92 is positioned atop the first layer 90. Thesecond layer 92 is a layer of the hollow glass microspheres 84. Thesecond layer 92 typically only includes the hollow glass microspheres84, although in some embodiments the second layer 92 may include acombination of the hollow glass microspheres 84 and the fibers 82.

Referring now to FIG. 19 , illustrated is another lightweight prepreghaving a layered configuration. Specifically, the lightweight prepregincludes a first layer 90 that includes a mat, web, or mesh of fibersand a third layer 94 that also includes a mat, web, or mesh of fibers82. The first layer 90 and/or third layer 94 may include any of thefiber configurations or arrangement illustrated in FIGS. 12-16 , and inparticular are typically woven fabrics, nonwoven mat layers, choppedfiber meshes, or any combination thereof. A second layer 92 ispositioned between the first layer 90 and the third layer 94. The secondlayer 92 is a layer of the hollow glass microspheres 84. The secondlayer 92 typically only includes the hollow glass microspheres 84,although in some embodiments the second layer 92 may include acombination of the hollow glass microspheres 84 and the fibers 82. Insome embodiments, the first layer 90 and the third layer 94 may belayers of hollow glass microspheres 84 and the second layer 92 may be alayer of the fibers 82.

In some embodiments, the thermoplastic prepregs described herein may notbe fully polymerized. As such, the thermoplastic prepregs may include aresidual resin content—e.g., a residual monomer or oligomer content. Theresidual resin content consists of monomers or oligomers that have notpolymerized into the thermoplastic material. For example, thethermoplastic material of a thermoplastic prepreg may include between0.5 and 5 percent of the residual monomers or oligomers, and morecommonly between 1 and 3 percent, or between 1 and 2 percent, of theresidual monomers or oligomers. The percentage of residual monomers oroligomers that is present in the thermoplastic material is determined inrelation to the amount of resin that was initially added to the fiberreinforcement. For example, a residual monomer or oligomer content ofbetween 0.5 and 5 percent means that 0.5-5 percent of the resin that wasadded to the fiber reinforcement remains in the unpolymerized state. Thecontent of residual monomer or oligomer in the prepreg can be measuredvia a solvent extraction method as descried herein below. For example,the amount of residual caprolactam in polyamide-6 prepreg can bemeasured via the extraction of grounded powder of prepreg using hotwater. The thermoplastic material of the thermoplastic prepreg may havea higher molecular weight than conventional thermoplastic prepregs. Forexample, the thermoplastic prepreg may include a higher molecular weightpolyamide-6 material. In such embodiments, the higher molecular weightthermoplastic material may be evidenced by a non-solubility of thepolyamide-6 material in a solvent in which conventional hydrolyticallypolymerized polyamide-6 resin is typically soluble. For example,polyamide-6 resin formed via in situ anionic polymerization ofcaprolactam may be insoluble in solvents such as hexafluoroisopropanol(HFIP), while the common hydrolytically polymerized polyamide-6 issoluble in HFIP.

The thermoplastic prepregs of FIGS. 12-19 may be roll products or may becut into individual segments as desired.

Methods

FIG. 2 illustrates a method 200 of forming a fully impregnatedthermoplastic prepreg product. At block 210 a fabric or mat is movedfrom a starting point to an ending point. The fabric or mat is subjectedto a plurality of processes between the starting point and ending pointand is in substantially constant movement between the starting point andending point. At block 220, the fabric or mat is dried to removeresidual moisture from one or more surfaces of the fabric or mat. Atblock 230, a monomer or oligomer is mixed with a catalyst and anactivator to form a reactive resin mixture. The catalyst and activatorfacilitate in polymerizing the monomer or oligomer to form athermoplastic polymer. In some embodiments, a portion of the monomer oroligomer may be mixed with the catalyst in a first tank and a portion ofthe monomer or oligomer may be mixed with the activator in a second tankthat is separate from the first tank. In such embodiments, mixing themonomer or oligomer with the catalyst and the activator comprises mixingthe materials from the first tank and the second tank in a static mixer.

At block 240, the reactive resin mixture is applied to the fabric ormat. The reactive resin mixture may have a viscosity of lower than 10mPa-s. At block 250, the reactive resin mixture coated fabric or mat ispassed through a calendar or press that presses the reactive resinmixture through the fabric or mat so that the reactive resin mixturefully saturates the fabric or mat. At block 260, the reactive resinmixture coated fabric or mat is passed or moved through a curing oven topolymerize the reactive resin mixture and thereby form the thermoplasticpolymer. During at least a portion of the above process, an environmentin the vicinity of the coated fabric or mat is controlled to maintain ahumidity in the air to substantially zero. Greater than 90%, 95%, 98%,or even 99% of the reactive resin mixture may be reacted to form thethermoplastic polymer.

In some embodiments, the method may also include applying amoisture-free gas to one or more surfaces of the reactive resin mixturecoated fabric or mat to control the environment in the vicinity of thefabric or mat. In a specific embodiment, nitrogen gas may be applied tothe one or more surfaces of the reactive resin mixture coated fabric ormat. In some embodiments, the method may further include winding thecured thermoplastic prepreg into a roll product. In some embodiments,the curing oven may be a double belt compression oven. In suchembodiments, block 250 and 260 may occur simultaneously.

FIG. 3 illustrates another method 300 of forming a fully impregnatedthermoplastic prepreg product. At block 310, a reactive resin is appliedto a fabric or mat, the resin being combined with a catalyst and anactivator that facilitate in polymerizing the resin to form athermoplastic polymer. The catalyst and activator may be housed inseparate holding tanks with or without the resin and may be mixedtogether with the resin prior to application of the resin to the fabricor mat. Alternatively, the catalyst or the activator may be pre-appliedto the fibers of the fabric or mat and the other material may be appliedto the fabric or mat with the resin. At block 320, the resin coatedfabric or mat is passed or moved through a calendar or press to fullysaturate the fabric or mat with the resin. At block 330, the resincoated fabric or mat is passed or moved through a curing oven topolymerize the resin and thereby form the thermoplastic polymer. Stateddifferently, the resin coated fabric or mat is passed or moved throughthe oven to polymerize the resin and thereby form the polymer. During atleast a portion of the above process, humidity in the vicinity of thecoated fabric or mat is maintained at substantially zero. In addition,the above process occurs in a time of 20 minutes or less, 10 minutes orless, or 5 minutes or less.

In some embodiments, the method further includes drying the fabric ormat prior to application of the resin to remove residual moisture fromone or more surfaces of the fabric or mat. In such embodiments, aninfrared heater, pre-drying oven, or other drying device may be used toremove residual moisture from the fabric or mat.

In some embodiments, the method further includes applying amoisture-free gas to one or more surfaces of the fabric or mat tomaintain the humidity in the vicinity of the fabric or mat tosubstantially zero. In such embodiments, nitrogen gas may be blownacross or onto one or more surfaces of the coated fabric or mat. In someembodiments, the method additionally includes winding the fullyimpregnated thermoplastic prepreg into a roll product. In some otherembodiments, the method additionally includes cutting the fullyimpregnated thermoplastic prepreg into sheets.

FIG. 20 illustrates a method 400 of forming a thermoplastic prepregproduct. At block 410, a fiber mesh is moved atop a lower belt of adouble belt press mechanism. The fiber mesh includes chopped fibers. Atblock 420, the fiber mesh is dried via a drying mechanism that ispositioned atop the lower belt and that is configured to remove residualmoisture of the fiber mesh. At block 430, monomers or oligomers areapplied to the fiber mesh via a resin application die that is positionedatop the lower belt. At block 440, the fiber mesh and the appliedmonomers or oligomers are passed between the lower belt and an upperbelt of the double belt press mechanism to press the monomers oroligomers through the fiber mesh and thereby fully saturate the fibermesh with the monomers or oligomers. At block 450, the fully saturatedfiber mesh is passed through a curing oven that is configured topolymerize the monomers or oligomers as the fiber mesh is moved throughthe curing oven and thereby form the thermoplastic polymer. The fibermesh is fully impregnated with the thermoplastic polymer uponpolymerization of the monomers or oligomers. The method may also includewinding the thermoplastic prepreg into a roll product or cutting thethermoplastic prepreg into sheets.

In some embodiments, the method may also include mixing the monomers oroligomers with a catalyst and an activator to form a reactive resinmixture. The catalyst and activator may facilitate in polymerizing themonomers or oligomers to form the thermoplastic polymer. The method mayalso include applying a moisture-free gas onto the fiber mesh after theapplication of the monomers or oligomers to substantially preventexposure of the monomers or oligomers to ambient moisture in thesurrounding environment. The top belt of the double belt mechanism maybe fully enclosed within the curing oven.

In some embodiment, the method may also include cutting fiber strands orrovings via a fiber chopper that is positioned above the lower belt toform the chopped fibers. The fiber chopper may be positioned so that asthe fibers strands or rovings are cut, the chopped fibers fall atop thelower belt and form the fiber mesh. In such embodiments, the method mayfurther include drying the fiber strands or rovings via a second dryingmechanism as the fiber strands or rovings are unwound from one or morespools and before the fiber strands or rovings are cut to form thechopped fibers.

The fiber chopper may be a first fiber chopper and the chopped fibersmay be first chopped fibers. In such embodiments, the method may alsoinclude cutting second fiber strands or rovings via a second fiberchopper that is positioned above the lower belt to form second choppedfibers. The second fiber chopper may be positioned so that as the secondfibers strands or rovings are cut, the second chopped fibers fall atopthe first chopped fibers and form a layered or hybrid fiber mesh.

The method may additionally include unwinding a fabric or nonwoven matfrom an unwinder and moving the fabric or nonwoven mat atop the lowerbelt so that the chopped fibers are positioned above or below the fabricor nonwoven mat and form a layered or hybrid fiber mesh that includes orconsists of the chopped fibers and the fabric or nonwoven mat. Thelayered or hybrid fiber mesh may be subjected to the drying mechanism,the resin application die, the double belt mechanism, and the curingoven so that the monomers or oligomers fully saturate the layered orhybrid fiber mesh and the thermoplastic polymer fully impregnates thelayered or hybrid fiber mesh upon polymerization of the monomers oroligomers.

In some embodiments, the method may additionally include applying asizing composition to the fibers of the fiber mesh. The sizingcomposition may have a coupling agent that promotes bonding between thefibers and the thermoplastic polymer. The fiber mesh may include glassfibers, carbon fibers, basalt fibers, metal fibers, ceramic fiber,natural fibers, synthetic organic fibers, aramid fibers, inorganicfibers, or combinations thereof. The monomers or oligomers may compriseor consist of lactams, lactones, cyclic butylene terephthalate (CBT),methyl methacrylate, precursors of thermoplastic polyurethane, ormixtures thereof. The lactams may comprise or consist of caprolactam,laurolactam, or mixtures thereof.

FIG. 21 illustrate a method 500 of forming a thermoplastic prepreg. Atblock 510, a fiber mat or web is moved atop a lower belt of a doublebelt press mechanism. At block 520, the fiber mat or web is dried via adrying mechanism to remove residual moisture from the fiber mat or web.At block 530, a lightweight filler material is applied to the fiber mator web via an application mechanism that is positioned atop the lowerbelt. The lightweight filler material is applied as the fiber mat or webis moved past the application mechanism. It should be noted that in someembodiments blocks 520 and 530 may be switched so that the lightweightfiller material is applied to the fiber mat or web and then the fibermat or web and lightweight filler material is dried via the dryingmechanism. At block 540, monomers or oligomers are applied to the fibermat or web via a resin application die that is positioned atop the lowerbelt. At block 550, the fiber mat or web, the lightweight fillermaterial, and the applied monomers or oligomers are passed between thelower belt and an upper belt of the double belt press mechanism to pressthe monomers or oligomers through the fiber mat or web and thelightweight filler material and thereby fully saturate the fiber mat orweb and lightweight filler material with the monomers or oligomers. Atblock 560, the fully saturated fiber mat or web and lightweight fillermaterial is passed through a curing oven to polymerize the monomers oroligomers and thereby form a thermoplastic polymer. The monomers oroligomers are polymerized as the fiber mat or web and lightweight fillermaterial are continuously moved through the curing oven. Uponpolymerization of the monomers or oligomers, the fiber mat or web andlightweight filler material are fully impregnated with the thermoplasticpolymer. The lightweight filler material may be applied to the fiber mator web so that the lightweight filler material is disposed only on afirst side of the fiber mat or web.

In some embodiments, the method may further include cutting thethermoplastic prepreg into separate sheets or pieces, which may bestacked atop one another. In other embodiment, the thermoplastic prepregmay be wound or rolled into a roll product. In some embodiments, themethod also includes mixing the monomers or oligomers with a catalystand/or an activator to form a reactive resin mixture. The catalyst andactivator facilitate in polymerizing the monomers or oligomers to formthe thermoplastic polymer. The method may further include applying amoisture-free gas onto one or more surfaces of the fiber mat or webafter application of the monomers or oligomers to substantially preventexposure of the monomers or oligomers to ambient moisture in thesurrounding environment.

In some embodiments, the fiber mat or web may include a woven fabric, anonwoven mat, a chopped fiber mesh, or any combination thereof. Forexample, the fiber mat or web may include a chopped fiber mesh that isformed by disposing chopped fiber strands on the lower belt of thedouble belt press mechanism. In such embodiments, the method may alsoinclude cutting fiber strands or bundles via a fiber chopper that ispositioned above the lower belt, or dispersing chopped fibers onto thelower belt via a fiber scattering unit to form a chopped fiber mesh. Thefiber chopper may be positioned so that as the fibers strands or bundlesare cut, the chopped fibers fall atop the lower belt, or atop a fibermat or web, to form the chopped fiber mesh. In other embodiments,chopped fibers may be dispersed or spread atop the lower belt, or thefiber mat or web, to form the chopped fiber mesh.

In some embodiments, the application mechanism that applies thelightweight filler material (e.g., hollow glass microspheres) atop thefiber mat or web is a powder applicator or device that is configured toapply the lightweight filler material to the fiber mat or web. In otherembodiments, the resin application die is the application mechanism thatapplies the lightweight filler material atop the fiber mat or web. Insuch embodiments, the light weight filler material is hollow glassmicrospheres and the method further includes simultaneously applying thehollow glass microspheres and the monomers or oligomers to the fiber mator web via the resin application die. The lightweight filler material,and/or the fibers of the fiber mat or web, may include a sizingcomposition having a coupling agent that promotes bonding between thelightweight filler material or the fibers and the thermoplastic polymer.

In some embodiments, the method may also include applying a second fibermat or web layer atop the lightweight filler material to form a layeredthermoplastic prepreg with multiple layers of the fiber mat or web thatare separated by a layer of the lightweight filler material. In suchembodiments, the method may further include applying the lightweightfiller material atop the second fiber mat or web layer to form anadditional layer of the lightweight filler material atop the second mator web layer. The fiber mat or web may include glass fibers, carbonfibers, basalt fibers, metal fibers, ceramic fiber, natural fibers,synthetic organic fibers, aramid fibers, inorganic fibers, orcombinations thereof. The monomers or oligomers may include lactams,lactones, cyclic butylene terephthalate (CBT), MMA, precursors ofthermoplastic polyurethane, or mixtures thereof. The lactams may includecaprolactam, laurolactam, or mixtures thereof. In some embodiments, thedouble belt press mechanism and the curing oven may be components of adouble belt oven.

Exemplary Materials and Systems

Uni-directional stitched fabric consisting of 1200 tex glass fiberrovings with the area weight of 670 g/m² were used for makingpolyamide-6 prepregs, using the system shown in FIG. 1A. Two heatedtanks were used for melting caprolactam-catalyst andcaprolactam-activator separately. 1,000 grams of caprolactam(Bruggemann, AP Nylon grade) and 74.0 grams of Bruggolen® C10 catalyst(containing sodium caprolactamate) were added to the first tank. Themixture of caprolactam and C10 was melted at 100° C. Separately, 1,000grams of caprolactam (Bruggemann, AP Nylon grade) and 27.0 grams ofBruggolen® C20 activator (containingN,N′-hexane-1,6-diylbis(hexahydro-2-oxo-1H-azepine-1-carboxamide)) wereadded to the second tank. The mixture of caprolactam and C20 was meltedat 100° C. The melts from the two tanks were then mixed at 1:1 ratio ina static mixer before the application of the reactive resin mixture onthe fabric through a slot die with the opening of 0.33 mm.

A double belt press oven with two Teflon-coated belts was used in theexperiments to press and cure the reactive resin mixture. The doublebelt press was electrically heated and the oven temperature was set at390° F. The line speed was set such that the residence time of thecoated fabric in the oven was approximately 3.5 minutes. The resinapplication rate was adjusted to achieve a target resin content of 30%in the prepregs.

Example 1

The experiment was run without infrared (IR) heating as shown in FIG.1A. The residual moisture on the fabric negatively impacted the anionicpolymerization of caprolactam. A significant amount of caprolactam fumewas observed at the exit of the double belt press oven; and sticking ofthe coated fabric to the belts was observed. The caprolactam fume at theoven exit indicates an incomplete polymerization of caprolactam.

Example 2

The experiment was run with IR heating and the fabric was heated to thetemperature of 330° F. prior to the application of the reactive resinmixture. The slot die was placed about 10 inches away from the inlet ofthe oven. No nitrogen purging or box enclosure was used to prevent theexposure of the coated fabric to ambient moisture. A significant amountof caprolactam fume was observed at the exit of the double belt pressoven; and sticking of the coated fabric to the belts was observed. Thecaprolactam fume at the oven exit indicates an incomplete polymerizationof caprolactam.

Example 3

The experiment was run with IR heating and the fabric was heated to thetemperature of 330° F. prior to the application of the reactive resinmixture. The slot die was placed within 1.0 inch from the inlet of theoven. Nitrogen was blown onto the coated fabric through perforated holeson a stainless steel tube, to prevent the exposure of the coated fabricto ambient moisture. Complete polymerization was achieved and minimalamount of caprolactam fume was observed at the exit of the double beltpress oven. No sticking of the coated fabric to the belts was observed.Scanning electron microscopy (SEM) analysis was conducted on theresulting prepregs to examine the impregnation. FIG. 4 is a typical SEMmicrograph of the cross-section of the prepreg, which indicates thecomplete impregnation of the fabric with thermoplastic polyamide-6resin.

As a person of skill in the art would readily understand, the residualmonomer or oligomer content in the thermoplastic prepreg can be measuredvia a solvent extraction method. For example, to measure the amount ofresidual monomer in polyamide-6 prepregs, powder samples may be preparedby cryo-grinding small pieces of prepregs in a grinder in the presenceof liquid nitrogen. Powder samples may then be extracted with water at150° C. using an Accelerated Solvent Extractor (ASE). The water in theextraction vials may then be evaporated in a turbo evaporator at 65° C.under a stream of nitrogen. The residues may be dried in a vacuum ovenat 55° C.; and then weighed to determine the amount of extractedmonomer. The conversion rate may be calculated based on the amount ofthe extracted residual monomer and the starting amount of monomer thatis used for the impregnation.

“ASTM” refers to American Society for Testing and Materials and is usedto identify a test method by number. The year of the test method iseither identified by suffix following the test number or is the mostrecent test method prior to the priority date of this document. For anyother test method or measurement standard defined or described herein,the relevant test method or measurement standard is the most recent testmethod or measurement standard prior to the priority date of thisdocument. Where a range of values is provided, it is understood thateach intervening value, to the tenth of the unit of the lower limitunless the context clearly dictates otherwise, between the upper andlower limits of that range is also specifically disclosed. Each smallerrange between any stated value or intervening value in a stated rangeand any other stated or intervening value in that stated range isencompassed. The upper and lower limits of these smaller ranges mayindependently be included or excluded in the range, and each range whereeither, neither, or both limits are included in the smaller ranges isalso encompassed within the invention, subject to any specificallyexcluded limit in the stated range. Where the stated range includes oneor both of the limits, ranges excluding either or both of those includedlimits are also included.

As used herein and in the appended claims, the singular forms “a”, “an”,and “the” include plural referents unless the context clearly dictatesotherwise. Thus, for example, reference to “a method” includes aplurality of such methods and reference to “the glass fiber” includesreference to one or more glass fibers and equivalents thereof known tothose skilled in the art, and so forth. The invention has now beendescribed in detail for the purposes of clarity and understanding.However, it will be appreciated that certain changes and modificationsmay be practice within the scope of the appended claims.

Also, the words “comprise,” “comprising,” “include,” “including,” and“includes” when used in this specification and in the following claimsare intended to specify the presence of stated features, integers,components, or steps, but they do not preclude the presence or additionof one or more other features, integers, components, steps, acts, orgroups.

What is claimed is:
 1. A thermoplastic prepreg comprising: a web or meshof fibers, the web or mesh of fibers including chopped fibers having afiber length and a fiber diameter; and a thermoplastic polymer that isfully impregnated through the web or mesh of fibers such that thethermoplastic prepreg has a void content of less than 5%, thethermoplastic polymer being polymerized monomers and oligomers in whichgreater than 90% of the monomers or oligomers react to form thethermoplastic polymer; wherein: the thermoplastic prepreg includes 5 to95 weight percent of the thermoplastic polymer; and the web or mesh offibers is not mechanically bonded and does not include a binder otherthan the thermoplastic polymer that binds the chopped fibers together.2. The thermoplastic prepreg of claim 1, wherein the thermoplasticprepreg further comprises hollow glass microspheres positioned atop theweb or mesh of fibers or dispersed within the web or mesh of fibers. 3.The thermoplastic prepreg of claim 1, wherein the chopped fibers includefibers having a fiber length of between 10 and 100 mm.
 4. Thethermoplastic prepreg of claim 1, wherein the web or mesh of fibersincludes a first layer of fibers formed of first chopped fibers and asecond layer of fibers formed of second chopped fibers, wherein thefirst chopped fibers and the second chopped fibers are not entangled orintermixed except for at an interface between the first layer of fibersand the second layer of fibers.
 5. The thermoplastic prepreg of claim 1,wherein the thermoplastic prepreg includes a fabric or nonwoven matlayer and a layer of the web or mesh of fibers positioned atop thefabric or nonwoven mat layer.
 6. The thermoplastic prepreg of claim 1,wherein the web or mesh of fibers includes multiple fiber types or fibersizes that are homogenously or uniformly dispersed within the web ormesh of fibers and form a hybrid fiber mesh.
 7. The thermoplasticprepreg of claim 1, wherein the thermoplastic prepreg includes multiplelayers of hollow glass microspheres, and wherein the multiple layers ofhollow glass microspheres are separated by the web or mesh of fibers. 8.The thermoplastic prepreg of claim 1, wherein the fibers of the web ormesh include a sizing composition having a coupling agent that promotesbonding between the fibers and the thermoplastic polymer.
 9. Thethermoplastic prepreg of claim 1, wherein the fibers of the web or meshinclude glass fibers, carbon fibers, basalt fibers, metal fibers,ceramic fibers, natural fibers, synthetic organic fibers, aramid fibers,inorganic fibers, or combinations thereof.
 10. The thermoplastic prepregof claim 1, wherein the thermoplastic polymer comprises nylon, PBT,PMMA, thermoplastic polyurethane, and combinations thereof.
 11. Thethermoplastic prepreg of claim 10, wherein the thermoplastic polymerconsists of thermoplastic polyurethane (TPU).
 12. A thermoplasticprepreg comprising: a web or mesh of chopped fibers; and a thermoplasticpolymer that is fully impregnated through the web or mesh of choppedfibers such that the thermoplastic prepreg has a void content of lessthan 5%, the thermoplastic polymer being polymerized monomers andoligomers in which greater than 90% of the monomers or oligomers reactto form the thermoplastic polymer; wherein: the thermoplastic prepregincludes 5 to 95 weight percent of the thermoplastic polymer; and theweb or mesh of chopped fibers is not mechanically bonded and does notinclude a binder other than the thermoplastic polymer that binds thechopped fibers together.
 13. The thermoplastic prepreg of claim 12,wherein the thermoplastic prepreg further comprises hollow glassmicrospheres positioned atop the web or mesh of chopped fibers ordispersed within the web or mesh of chopped fibers.
 14. Thethermoplastic prepreg of claim 12, wherein the web or mesh of choppedfibers includes a first layer of fibers formed of first chopped fibersand a second layer of fibers formed of second chopped fibers, whereinthe first chopped fibers and the second chopped fibers are not entangledor intermixed except for at an interface between the first layer offibers and the second layer of fibers.
 15. The thermoplastic prepreg ofclaim 12, wherein the thermoplastic prepreg includes a fabric ornonwoven mat layer and a layer of the web or mesh of chopped fiberspositioned atop the fabric or nonwoven mat layer.
 16. The thermoplasticprepreg of claim 12, wherein the web or mesh of chopped fibers includesmultiple fiber types or fiber sizes that are homogenously or uniformlydispersed within the web or mesh of chopped fibers and form a hybridfiber mesh.
 17. The thermoplastic prepreg of claim 12, wherein thethermoplastic prepreg includes multiple layers of hollow glassmicrospheres, and wherein the multiple layers of hollow glassmicrospheres are separated by the web or mesh of chopped fibers.
 18. Thethermoplastic prepreg of claim 12, wherein the fibers of the web or meshof chopped fibers include glass fibers, carbon fibers, basalt fibers,metal fibers, ceramic fibers, natural fibers, synthetic organic fibers,aramid fibers, inorganic fibers, or combinations thereof.
 19. Thethermoplastic prepreg of claim 12, wherein the thermoplastic polymercomprises nylon, PBT, PMMA, thermoplastic polyurethane, and combinationsthereof.
 20. The thermoplastic prepreg of claim 19, wherein thethermoplastic polymer consists of thermoplastic polyurethane (TPU).